Keyboard layout issue

Playing Minecraft is just fine and dandy, including sending messages etc.

After some time, however, keyboard layout seem to change or key assignment of the letter "a" for some reason to send some sort of control character instead of the "a", when trying to use the console to send commands or simple text to fellow players.

The effect is as if I have selected everything until the beginning of the text line, so that the next keystroke would remove everything already typed, and continue with the one that has been entered.

Restarting Minecraft fixes the problem until some time into playing.