Backstory and Explanation:
I've seen this bug on the bug tracker before, and it says it's fixed, however, it isn't fixed for every desktop environment/window manager, for example, I'm running dwm, a minimalist window manager made by suckless. When I first switched to it and first started playing minecraft in it, I noticed this pretty quickly, but I hadn't noticed it on pop shell, so I assumed it was a bug with minecraft running on the window manager.

Reproducing This Bug:
1. Open any linux distribution while running dwm as your window manager
2. In any text field, hold ctrl and press a, this replaces the entire text field with a, you can also do this for other button combinations such as ctrl+c and ctrl+v (in which v is added to the end of the pasted string), it even works with things that wouldn't normally do anything, like ctrl+g, typing g instead of doing nothing

Conclusion:
I'm assuming this is a bug in which minecraft doesn't realize it isn't supposed to insert these characters while the ctrl button is being held, so it should be a relatively simple fix, however, I'm not exactly sure why it affects dwm and no longer affects most desktop enviornments, but I'm not a code developer, so I wouldn't know anyways