http://bugs.winehq.org/show_bug.cgi?id=17565
--- Comment #4 from Fab netfab@gmail.com 2009-10-15 11:09:47 --- I'm talking about Half-Life 1 engine, I haven't try with Half-Life 2.
This seems to have something to do with the numpad. When in game, turning on/off the numpad with the numlock key pause/unpause the game. When the numpad is off, all numpad keys still works. When launching the game with numpad off, the game doesn't pause on first key pressed.