Does moving into an opponent's square generate an Attack of Opportunity when you do so with a 5-foot step?

Question

This question is relevant specifically to creatures with a reach equal to 0', as they have to go into opponents' squares in order to attack. From Big and Little Creatures in Combat:

Tiny, Diminutive, and Fine Creatures: Very small creatures take up less than 1 square of space. This means that more than one such creature can fit into a single square. A Tiny creature typically occupies a space only 2-1/2 feet across, so four can fit into a single square. 25 Diminutive creatures or 100 Fine creatures can fit into a single square. Creatures that take up less than 1 square of space typically have a natural reach of 0 feet, meaning they can't reach into adjacent squares. They must enter an opponent's square to attack in melee. This provokes an attack of opportunity from the opponent. You can attack into your own square if you need to, so you can attack such creatures normally. Since they have no natural reach, they do not threaten the squares around them. You can move past them without provoking attacks of opportunity. They also can't flank an enemy.

So these creatures usually have two chances to generate attacks of opportunity (AoO) while moving when attacking, one for leaving the threatened square in front of the opponent, and another for entering into the opponent's square (this AoO only for the opponent). You can avoid though the first with a 5-foot step:

Moving: Moving out of a threatened square usually provokes attacks of opportunity from threatening opponents. There are two common methods of avoiding such an attack—the 5-foot step and the withdraw action.

But the second one is not generated by going out itself but by the action of geting into the opponents square. The 5-foot step rule text says though:

Take 5-Foot Step You can move 5 feet in any round when you don't perform any other kind of movement. Taking this 5-foot step never provokes an attack of opportunity. You can't take more than one 5-foot step in a round, and you can't take a 5-foot step in the same round that you move any distance.

So, technically it just means the 5-foot step action does not generate an AoO by itself. Never. But does conditions that produce the 5-foot step action itself generate? The going out of threatened is clearly stated in the rules as no, but in the case of going into occupied square it is not clearly stated.

Answer 1

A creature that, because of the creature's size, provokes attacks of opportunity for entering a foe's square provokes attacks of opportunity when entering that foe's square even if the creature enters that square by taking a 5-ft. step...

The rules cited in the question are from two different places about two different things. The 5-ft. step rules don't care about the creature size rules, and the creature size rules don't care about the 5-ft. step rules. The two rules are managed independently and don't interact. Thus, when a Tiny, Diminutive, or Fine creature enters an opponent's square, it provokes an attack of opportunity even if it entered that opponent's square by taking a 5-ft. step. That's a function of the creature's size exclusive of the creature's 5-ft. step.

Example 1
A Tiny, Diminutive, or Fine creature takes a 5-ft. step when adjacent to opponent and within that opponent's threatened area that doesn't provoke an attack of opportunity (because of the 5 ft. step) and moves into his opponent's square which does provoke attacks of opportunity (because of the creature's size).

When a Tiny, Diminutive, or Fine creature takes a move action to move within its opponent's threatened area then enter its opponent's space, the creature probably should provoke attacks of opportunity twice, once for the movement within the creature's threatened area and once for entering the creature's square, except that the FAQ (see below) says to treat the opportunity granted by moving within a creature's threatened area as part of the same movement needed to enter a creature's space. Thus a typical Medium creature gains only one attack of opportunity against a Tiny foe that takes a move action to enter the creature's square.

Example 2
A Tiny, Diminutive, or Fine creature takes a move action to travel 30 ft. to enter an opponent's square. The creature provokes an attack of opportunity when moving within the opponent's threatened area as normal then can enter the opponent's square with impunity.

It's sort unfortunate that two attacks of opportunity aren't provoked. It might've saved the Dexterity 13 commoner with the feat Combat Reflexes from death by house cat.

...And the FAQ agrees

The Pathfinder Roleplaying Game Core Rulebook FAQ contains the following exchange:

Question: In the section on Tiny and smaller creatures, it says that entering a creature’s space provokes an attack of opportunity, but typically 5-foot steps don’t provoke an attack of opportunity. If a Tiny or smaller creature took a 5-foot step into a creature’s space, would it provoke an attack of opportunity?
Answer: Yes. Even with a 5-foot step, a Tiny or smaller creature entering a creature’s space provokes an attack of opportunity (unless it is using a more specific ability to avoid the attack of opportunity such as the Monkey Shine feat). This doesn’t mean that a Tiny or smaller creature entering a creature’s space and moving out of a threatened square with a move action provokes two attacks of opportunity from that creature, for the same reason that moving out of multiple of a creature’s threatened squares in the same move action doesn’t provoke two attacks of opportunity.

This exchange was added to the FAQ in Jan. 2016.

Answer 2

No. The 5-foot step rule's no-AoOs clause does not specify any particular type of attack-of-opportunity provocation, it simply negates any attacks of opportunity which may otherwise have been forthcoming due to taking the "5-foot step" action. Therefore, by strict interpretation of the RAW, the attack of opportunity for entering an enemy's space as a tiny or smaller creature is negated by the 5-foot step rules, and you are able to close without retribution.

Note that setting this up without taking more attacks than if you'd just eaten the AoO is somewhat difficult, as it will usually involve approaching adjacent to the enemy, then spending an entire enemy turn there before being able to adjust into their space. It is, however, useful in conjunction with certain unusual movement abilities, as well as for tiny creatures able to hide well enough to ambush someone who made it within 5 feet of them without becoming aware of them. As gatherer818 pointed out, this also prevents a Small or larger creature from taking a 5-foot step every turn to force a Tiny or smaller opponent to provoke AoO every turn.