How do multiple-round touch spells work?

Question

I'm the GM for a group of four people, two of whom are deviously creative. This time, this dynamic duo is playing a pair of 7th-level druids, both of which had taken the spell Produce Flame for the day.

This spell enables the caster to deliver a few touch attacks for some good damage (for low level characters, at least):

You can strike an opponent with a melee touch attack, dealing fire damage equal to 1d6 + 1 point per caster level (maximum +5).

That's good. However, the the touch spell rules reads:

You must touch a creature or object to affect it. A touch spell that deals damage can score a critical hit just as a weapon can. A touch spell threatens a critical hit on a natural roll of 20 and deals double damage on a successful critical hit. Some touch spells allow you to touch multiple targets. You can touch up to 6 willing targets as part of the casting, but all targets of the spell must be touched in the same round that you finish casting the spell. If the spell allows you to touch targets over multiple rounds, touching 6 creatures is a full-round action.

Emphasis mine.

That bolded line on the above rule is becoming problematic on one of my games.

Touching someone is normally resolved as an attack roll as part of the casting of the spell, or maybe as a standard action on another round. However, by the rule above, someone with a touch spell ready could touch 6 targets on the same round, as a full round action. That line doesn't even mention that the targets must be willing, so, in theory, a 6th level druid could hit 6 targets with a full round action, dealing 1d6+5 damage to each one of them, with a lvl1 spell.

The things get a bit worse when you consider that those 6 creatures don't need to be different creatures, as the rules never call to it on any point.

So, what's happening is that by the (liberal) reading of my players, a 6th level druid have with Produce Flame something akin to a Flurry of Blows, just... way better.

I feel the rules are not supposed to work like that, but as the RAW reads, how this exactly works?

Answer 1

There is a difference between a spell that says "You can make melee touch attacks", such as Produce Flame and spells (for example, Shadow Walk) that have as their target "Creature(s) touched".

The rules you quote above, where you can touch up to 6 creatures, refer to the latter; that is, spells that have "creatures touched" in their Target: line

Spells that allow you to make Melee Touch Attacks use the regular rules for making melee attacks, and will only allow attacks based on your BAB. Which is 1 per turn for 6th level Druids.

Answer 2

As you quoted, the touch spell rules say

Some touch spells allow you to touch multiple targets. [...]

You can touch up to 6 willing targets as part of the casting, [...]

If the spell allows you to touch targets over multiple rounds [...]

The spell description says

You can strike an opponent with a melee touch attack

So this particular spell isn't one of the some that allow multiple targets.

Also, it specifies a (melee/ranged) touch attack, which as defined elsewhere, uses the usual attack action.