bandpopup tab key works wrong

I have a bandbox with a bandpopup component where I put 2 textboxes (search criteria) a button (search button) and a listbox (result data).
When I open bandpopup the focus is on the first textbox. I press TAB key and I'm expecting the focus goes on the second textbox.
But what happens? The focus goes on the next input field in the same area where bandbox is.
That is, it seems that pressing TAB key on a bandpopup of a bandbox acts as if we press TAB directly on the bandbox input field.
And this happens even if bandbox is set as "readonly".