When I write on any type of sign, the background of the letters are transparent

When I type on any type of wooden sign and hit esc to finish, a rectangular or square selection that is positioned behind the letters becomes transparent so that I can see the blocks behind it but only through the letters. I haven't found anyone else that's had the same problem so I'm kind of desperate since most of the time it makes the letters unreadable.

As you can see in these pictures below, the bug shows everything behind the sign