One for the date experts

I am using the european date format "dd/mm/yyyy". My computer's system clock and worksheet cells are set to be the same. When I enter 22/06/2001 into a textbox on an Excel userform, the value is transfered to a cell on the worksheet. Great upto now! The date is mysteriously changed to mm/dd/yyyy when the entered "dd" is less than or equal to 12 (12 month in a year) eg 10/07/2001 changes to 07/10/2001. If the "dd" is >12 the date is left aligned on the worksheet as entered but not recognised as a date. Can anyone help with this twister?