(In reply to Andy Furniss from comment #3)

> I can see there are more artifacts than with vdpau m/a deint - I was
> expecting them to use the same underlying code and so have the same
> artifacts?

After looking at more samples it seems that sometimes parts of one of the
fields ends up with old content being displayed/not updated.

This is more than a few extra artifacts - it's buggy. With vdpau there were
artifacts, but you wouldn't notice them watching normally (would need to
pause/slow mo). Given the right input this is instantly noticeably corrupt.