This bug was fixed in 25w34a along with the Statistics menu redesign:
I believe this now only changes the game mode and commands for other players; there are now separate options for the world host in the “World Options” menu, accessed from the general options screen.
Can confirm as well. This probably has to do with the changes made to GUI edit boxes in 26.4 Snapshot 7. Now when navigating with arrow keys, any edit boxes you select will be unfocused and you need to press Space or Enter to focus and be able to write in them. This seems to have unintentionally affected the sign and hanging sign interfaces as well.