What happens when a creature loses its next move action?

Question

The feat Undermountain Tactics allows the use of the tactical maneuver stair king, which says

To use this maneuver, you must gain the high ground bonus on your attacks against an opponent. If you hit your foe with two or more melee attacks during your turn, he must make a Balance check (DC 10 + your Str modifier) or be knocked prone. Your opponent can opt to succeed automatically on his Balance check. If he does so, he will lose his move action on his next turn, but he will succeed automatically on Balance checks to resist this maneuver until the start of his next turn. Your opponent must make this choice before seeing the result of his Balance check. You can target a particular creature with this maneuver once per round. (Dungeonscape 46)

Emphasis mine. After opting to succeed automatically on the Balance skill check, what actions can a creature take on its next turn having lost its move action? For example, on its turn can the creature that opts to succeed automatically on the Balance skill check still take the full attack or withdraw actions? For example, having only lost the first move action due to opting to succeed automatically on the Balance skill check, on its turn can the creature still take its second move action?

The feat is rarely mentioned in optimization circles, and there is no Dungeonscape errata. (But, O, would that there were!) If it matters, I'm looking at the feat Undermountain Tactics for a mounted combatant—the attack bonus from high ground is gained by the rider against defenders on foot that are littler than the rider's mount. (Further, although shadier and likely worth its own question, because the rider shares the entirety of the mount's space, a rider with a significant mount should be able to employ the tactical maneuver door sentinel for much larger quantities of door.)

I've tagged this rules-as-written because that's preferred—perhaps such an answer can be teased from an effect using similar language elsewhere in the game—, but I understand this might be impossible. If it is, careful analysis, tabletop experience, or speculation is acceptable.

Answer 1

Starting from the beginning:

Action Types

In a normal round, you can perform a standard action and a move action, or you can perform a full-round action. You can also perform one or more free actions. You can always take a move action in place of a standard action.

A creature without a Move Action is thus left with its Standard Action and Free Actions (as well, I suppose, as its Swift/Immediate Actions).

The status of Full-Round actions is not clear, yet.

Move Action

[...]

You can take a move action in place of a standard action.

A creature can always use a Move Action instead of a Standard Action

Full-Round Action

[...]

Some full-round actions can be taken as standard actions, but only in situations when you are limited to performing only a standard action during your round. The descriptions of specific actions, below, detail which actions allow this option.

Restricted Activity

In some situations, you may be unable to take a full round’s worth of actions. In such cases, you are restricted to taking only a single standard action or a single move action (plus free actions as normal). You can’t take a full-round action (though you can start or complete a full-round action by using a standard action; see below).

A creature can only take a Full-Round Action as a Standard Action:

• if it is limited to performing only a Standard Action
• if it is explicitly specified that this particular Full-Round Action can be accomplished as a Standard Action

RAI¹: while not fully spelled out, it seems to me that being denied its Move Action (or having traded it off) falls under the case of Restricted Activity here, with only the Standard Action (and Free/Swift/Immediate Actions) remaining, similar to the Staggered condition.

Now, we can check the specific actions mentioned:

Full Attack Action

There is no specific mention of being able to make a full attack as a Standard Action, thus it does not seem possible.

Withdraw

Specifically for the Withdraw action, there is a rule:

Restricted Withdraw

If you are limited to taking only a standard action each round you can withdraw as a standard action. In this case, you may move up to your speed (rather than up to double your speed).

So it is possible to withdraw, although the maximum distance is halved.

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¹ I interpret the loss of the Move Action as a corresponding loss of time/energy, making the creature incapable of taking a full round's worth of actions on its next turn. It seems consistent with the one other condition that denies one its Move Action (Staggered).