I didn't found this reported anywhere, so I registered just to bitch about it (kidding).
I was playing Angel of shotgunnery and trying to be a true Ash Campbell when I noticed that while attacking with the chainsaw time didn't pass. So I could attack in melee forever totally unattacked until the monster was dead. Also works with a combat knife. The game gives the "This is a weapon for wimps, not a true man!" message, and the marine punches the monster (sound of fists is heard, damage really low), and time does not pass at all.
version: 0.9.9.2
platform: arch linux
PS: fu**ing awesome game!
EDIT: it also happens in Angel of Marksmanship and in both modes with forbidden weapons (like a chaingun)
EDIT2: changed the title to better reflect the bug