This looks like (automatic) block completion (or one of the other completions the IDE offers). I assume you have a repeat
somewhere in your code and that repeat
block is not properly closed with an until
, so block completion tries to close it, somehow, by putting an until ;
at the cursor each time your press return.
Either complete your code properly, or switch off block completion, e.g. from the main menu:
Tools -> Options -> Editor Options -> Code Insight -> [ ] Block completion
FWIW, I personally always leave it on, even if it can be a nuisance sometimes, because it shows me when I made a typo or similar mistake, and it usually takes away some of the typing I would have to do otherwise.