Do you have any .KeyPress events in the "bad" Form ? Any chance you're NODEFAULTing on the ENTER key stroke ?

Or, perhaps there's an ON KEY LABEL ENTER active ... or there's a Menu Item that uses ENTER as a hot key ... or some .Valid, .When, .GotFocus, .LostFocus is redirecting ...

>SET("confirm") is ON
>If I add a plain textbox with no formatting and no datasource I have the same problem, if I copy any of the 'non enter' textboxes to another form they work fine. It seems to be at form level.