eg.: When you have a form with 3 text-input field which are all required and you do this:

• type text in input1
• type text in input2
• type text in input3
• back to 1, delete text
• click 2 (no errormessage apears on 1)
• delete text input2
• click 3 (an errormessage apears on 2)
• delete text input3 and click input1 or input2, (no errormessage apears on 3)

when you click back to input1 and add text, click input3 and add text (no errormessage apears on input1), click input1 or 2 (an errormessage apears on 3).

There are variations on this. Sometimes he errors only the last input.

So, in short: The onblur event or the validation process after the onblur, for required field, seems to be defect.