Thanks for reporting this. I reproduced the problem and have fixed it.
During live resizing, ListBox was discarding later custom paint requests whenever a paint callback was already pending. The original callback then completed using an earlier g.Width and g.Height, leaving row backgrounds lagging behind or incompletely painted.
ListBox now remembers that another repaint is needed and runs one final callback with the latest dimensions. This avoids building an unbounded paint backlog while ensuring the settled ListBox is fully painted.
The fix covers PaintCellBackground, PaintCellText, PaintHeaderBackground, and PaintHeaderContent.
The fix will be included in the next release: https://feedback.objo.dev/bug/1301
