CListCtrlEx::OnEraseBkgnd (with m_bSkipEraseBkgnd) only erases the empty
area below the last item, not the horizontal strip right of the last
column (the ~20px scrollbar reserve AdjustColumnWidths always leaves).
Changing the column count via SetColumnVisible/ToggleColumnVisibility
redistributed widths but never repainted with background erase, so stale
pixels from the previous last column lingered next to the new one (e.g.
after "TLS") until a tab switch or minimize/restore forced a full redraw.
Mirror the proven OnSize needRefresh path: temporarily lift the
skip-erase flag and issue a full RedrawWindow with
RDW_ERASE|RDW_INVALIDATE|RDW_ALLCHILDREN|RDW_UPDATENOW after each
visibility change.
Co-Authored-By: deepseek-v4-pro
