Ah yes, the rigors of urban combat à la OFP
Gotta face it...the engine ain't really built for it (observe that throughout all of BIS's official missions, not ONCE was there a single person inside a house...not even Guba's mansion!). However, there is a solution to it:
unit setUnitPos "UP"
<- will force unit to stand at all times, thus eliminating the falling-through-floor thing (sometimes when put to 4x speed, you can even run through walls...fancy that...).
Oh, since they're already made aware 'tis not a problem, but observe that at least in 1.46 if you put a unit into the "UP" mode while they're safe, they're unable to unsling their weapons and start shooting
Bugger that.
Other modes are "DOWN" and "AUTO" (self-explanatory)
good luck!
Wolfrug out.