Of course :) after insert task I have added...

my $trim = $listbox->size - $maxlines;
$listbox->delete(0, $trim-1) if trim > 0;
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I accept the point re last-read-to-seek-delay-data-loss: any ideas anyone?

Otherwise I don't see any harm with the seek(F,0,1) - isn't it required in order to clear the EOF condition as per docs?