Have you tried using append and clear or del, rather than setting to a new empty list?

I.e
tableview.selected_rows.append((0,1))

And either

tableview.selected_rows.clear()

Or
del tableview.selected_rows[:]

To clear it.

I can imagine a scenario where the selected_rows object is linked in some way to the native iOS list, and so just setting to a new object doesn't actually clear the old one..