Backspacing over a number to empty the field then pops up a dialog saying "please enter a number". Hitting enter to clear it pops it up again. Closing it with the mouse takes care of it, but it would be nice if hitting enter would also make it go away.
If you happen to have blank field and you want to type a negative number in, you have to put the number in first, then hit the minus sign. Perhaps it should only parse upon hitting enter or exiting the field as to avoid this error.