Whenever I pull up chat and try typing the letters "A", "C", "V", or "X" the chat will auto-select, auto-copy, auto-paste, or auto-cut the text respectively. This only happens in chat in minecraft and not in any other programs such as word, this forum, etc. Its almost as if Minecraft chat has the key bindings set to use the command function upon typing these letters. I've googled and haven't been able to find any solutions. I've also checked my keyboard settings and haven't found any hints.
https://bugs.mojang.com/browse/MC-3643
Basically, hit the 'command' key, and it clears the issue. (It happens for me when I switch away from Minecraft and then come back. Easy fix, though.)