When I write text in text boxes (I tested with naming world, superflat preset and structure block)
Legend: -Bugged, -Not bugged, -Oddly Bugged, -Oddly
When I write "a", it clears when I write next letter ( Oddly, when i write "ą" (I'm polish), it don't clear)
When I use <- or ->, it moves to an end of text box.
When I use backspace, it clears ALL text that is BEFORE. (Test:

 Crtl+Shift+A 

b (The b is not deleted)