QTreeView::indexRowSizeHint behaves wrong with setFirstColumnSpanned

Right now, QTreeView doesn't respect the sizeHint() of the delegate for a row with setFirstColumnSpanned() if first column is not in a visible part of the viewport.
For example. I have a delegate for a first column that draws rows with bug height. If i scroll viewport so i won't be able to see first column, QTreeView won't respect that delegate's sizeHint() and shrinks spanned row (so the info, painted by that delegate gets cut).
QTreeView should not only respect visible delegates, but delegate for a first column if setFirstColumnSpanned is set to true.