The mouser's underfoot assault (leaving the space clause)-How does it work?

The mouser can move within her foe's space and leave the foe's space unhindered and without provoking attacks of opportunity, but if the foe attempts to move to a position where the mouser is no longer in its space, the movement provokes an attack of opportunity from the mouser. This deed replaces opportune parry and riposte.

I've seen three different readings for this

1) The author didn't k now that tiny creatures threaten their own square and the ability is redundant

2) The ability creates a new, separate opportunity to take an attack of opportunity

3) The ability negates things that would normally allow the creature to leave the mouser's square without providing a movement related attack of opportunity such as the withdraw or 5 foot step.

1 seems unlikely and would create hurt feelings for a broke ability a mouser gave up opportune Parry and riposte to get.

3 is how I initially interpreted it, but over time I have come to the belief option 2 is the correct one as mobs will just provoke with a move rather than 5' step or withdraw basically granting no benefit if the GM metagames that all mobs know what underfoot assault is and leaving provokes.

FAQ worthy IMHO

I'm for three as well. Although I don't think it would negate an acrobatics roll , since at least that way they're beating you fair and square.

I used to play my mouser according to #2 but the Tiny/5' FAQ made me rethink it since although the AoO's have different triggers, both the triggers are movement related and it's one action happening to get out of my square.

Since then, been playing it #3 to take advantage of 5' steps out and withdraws. Some evil fun right there!

It's option 2, but the new FAQ on tiny AoO indicates that a 5ft step and withdraw wouldn't negate the option 2 AoO.

I used to play my mouser according to #2 but the Tiny/5' FAQ made me rethink it since although the AoO's have different triggers, both the triggers are movement related and it's one action happening to get out of my square.

Since then, been playing it #3 to take advantage of 5' steps out and withdraws. Some evil fun right there!

Unchained rogue + mouser is pretty sick. Attempt to 5 foot step away, sneak attack, halve their movement and stop 5 foot steps.. including that one they were trying to take.

all creatures not tiny creatures.. grumble neccesary but evil editing window grumble