That probably happened because you had 2 squads in the HT. Load 1 and it will probably be fine.
I guess it also a way to reduce the "drive by" shooting effect since having 4 or 6 lmgs(UKF),2 flamers,... out of HT can be allot more trouble than the current "bug".
He specifically mentions soviet M3.
2 squads can not go into it.