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Small graphical bug: Flipping off while firing sawn-off causes you to have three hands.
You also have three hands when firing shorty and M16 while flipping off.

Okay, I tested. The crash on getting 50% kills on maps happens when you quit game, start the game again and load the save.
What also happens is you don't get teleported back at the start of the level when you die and instead you just load the save.

While playing I've noticed two things.
First of all sometimes you can't reload your weapon and if you do it reloads way less ammo than it should.
Secondly, if you load a saved game and die you load the save and getting 50% kills on map crashes the game.