I change the clock preferences to show in the form 13:00:00, and it looks just fine, but then as soon as I press the close button, it returns to a custom format that contains no text. If I then go to preferences again and enter in %T for the time and %c for the tooltip, it works, so I will use this as a workaround, but this is very buggy and it should work if I select something other than a custom format.

Mint XFCE Sarah on a Gateway netbook LT4004u