QHeaderView / QTableView does not autoscroll properly when dragging movable columns, with ScrollPerPixel enabled

Situation: QTableView with more columns that can fit in the viewport.
Header columns are movable.
Scroll mode is set to per-pixel, as some columns may be quite wide.

Problems while dragging a column (with the header):
 * Table scrolls horizontally very slowly.
 * Table does not scroll to the right if the first column is partially
   visible (ie cut off at the left edge).