Vista - RequireFieldValidator and RangeValidator "strange" behaviour

Hi:

I have both validators on a certain field. The strange behaviour is like
this:

If I input a value greater than the max value defined in the RangeValidator
and press the submit button on the form, the error text of the
RangeValidator will flash once, then disappear. If I press the submit
button the 2nd time, the error text of the RangeValidator will appear and
stay on the screen, as it should be. Similar behaviour occurs when I just
tab away from the field after inputing a value bigger than the max.

Is this a bug? Or should I just ditch the validator and write my validation
code?

I'm using VB, VS2005, IE7 browser

Any pointer appreciated.