Has anyone else had this sort of error?

I have built a userform that collects info in textboxes
and then draws a chart. It works - usually.

Intermittently (though repeatable - first instance of form
only?), if the user navigates with the TAB key it actually
puts a TAB character into the control. The control was
setup with TabKeyBehavior = False and I have even put this
explicitly into the iniatlisation code. Infact on debug
even when the control is accepting TAB characters the
behavior is correctly set false so it is a bug of sorts??

Any ideas?

I am going to code around it by capturing and checking
value of control before manually moving focus to next
control but this is a basic function that goes to the
heart of using userforms.

Cheers
Paul