AltGr seems to lock

When typing commands that contain "@", "[", "]", etc. (german layout, quertz) which i need the AltGr key for everything typed so far disappears from the chat line. Really anoying especially because you can't properly type selectors. I hope it's a Minecraft issue otherwise I've got a problem

EDIT:
It happens when I type "a" after I've pressed AltGr once. It doesn't happen if I press it a secound time.