Jozsef Augusztiny

Still broken in 1.9.2, also effects players on servers who are not operators

I just found a fix from 4 years ago by u/darkfalzx on the subreddit

"Here is how to fix it. I have the same exact issue. When you open minecraft, before pressing F11, resize your minecraft window (larger or smaller, it doesn't matter), then hit F11 - that's it. Enjoy."

source: https://www.reddit.com/r/Minecraft/comments/i22w2/rminecraft_please_help_me_whenever_i_press_f11_to/c20cjho