Warning: this post contains spoilers, but is relevant to the issue at hand.
Just a heads up to everyone, when you get to Spoiler:
Mine crashed when I opened the door to get out of the room with the incinerator fire and was unable to recover my save.Don't know if this was the cause, but it was near the end of the 1st chapter and I just used the wonderful CH Unlock all chapters option and moved on to chapter 2.
Is there any chance you can add an option to rest ammo to 1? If you start a mission with only 1 knife, the unlimited ammo stops you from beign able to pick up anymore, which stops you from being able to throw them, since you cant throw them until you pick another up.
From best I can tell throwing knives seems to only work when you are a certain distance away from an enemy. The trainer is not affecting your ability to throw them, your distance from an enemy might be the culprit. When I've try to throw them close up, I get a melee attack, when I'm farther away, he throws the knives.