You apparently have auto-correction switched on. You can change that at Tools->autocorrect.
That is also the place where you can customize autocorrection for example by specifying not to capitalize after a comma. Andreas PS: of course by default Gnumeric should not want to autocorrect after comma. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]

