Text control bug.

After some time, everything I type in Minecraft acts as if my control key is held down (for example: if i press "a", it marks the whole text instead of writing an "a"). This makes it impossible to write and i have to restart the entire game. It ussually hapens after ca. 10 minutes. I've tried updating to Java 8 but when i try to launch MC it tells me to install Java 1.6. Hope this is enough!