Both TabStrip and TabStripPage has properties CausesValidation and ValidationGroup.
If user uses TabStrip's properties then TabStripPage's properties are ignored.
If TabStrip.CausesValidation = true then user will be unable to switch tabs until validator isn't valid. If user will use TabStripPage's properties then he will be able to switch to PREVIOUS tab and unable to switch to NEXT tab until validator isn't valid - this behavior useful for wizard-like interfaces.