Problem with ValidationGroup Property

[Guest]

Hi. I have an aspx page w/2 update panel controls UpdatePanel1 & UpdatePanel2.

UpdatePanel1 uses validationgroup="a" for all of it's validation controls &
button controls. UpdatePanel2 uses validationgroup="UsedVehicle" for all of
it's validation controls and button controls.

When I click a button control in UpdatePanel2 only controls having
validationgroup="usedvehicle" are validated - This works correctly.

But when I click a button control in UpdatePanel1 all controls (both with
validatoingroup="a" & validationgroup="UsedVehicle" are validated - This is
wrong only controls having validationgroup="a" should validate.

My code is lengthy so I haven't posted it initially. I was hoping someone
could let me know what I'm doing wrong. Any ideas? Thanks