Sometimes when opening the allies chat for the first time there already is a "t" present (how many times we not say "t9"). Here is a way to reliable reproduce the issue at my machine:
Host a game
Join with another player => press ready => type something in gamesetup chat so the chat is focused (with joiner)
press "t" with joiner
This is due to SDL_TextEvent being set when we focus the chat, but never stopped when switching pages, so SDL still passes the textevent to the input field and thus creates a "t". This is fixed by explicitly stopping the textEvent when switching gui pages using the Destroy function.