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.