Why EO validate is called twice with wrong values?

Question

I'm working with ADF BC 10.1.3.4 I have a page with af:table (editable) with Commit button. I've added a custom method validation on the underlying Entity Object (Attribute Validation), If wrong value inserted & commited, the validate method is called twice, and I have a duplicated error message on the UI. Also, after updating the cell to a valid value, the validate method is called with null value, or the old invalid value.