I've managed to duplicate this a couple of times just now. I could look at the code if we were all curious enough about what exactly is going on. Without looking at the code, I'd guess that it's something to do with the sequence of logic - maybe this:
Normally the game checks for jump bonus at the moment of a jump's peak.
If you bounce on a wall after a jump's peak, the bonus checks normally.
If you bounce on a wall before the jump's peak, bonus is never checked for.
If you happen to position yourself so that a bounce and bonus check happen in the same frame... maybe the flag to check the bonus gets set (maybe the bonus gets checked as well), but then the bounce happens and prevents the next step of logic (display & tally the bonus) from being triggered until after you land. At that point it uses Jumpman's landing coordinate instead of his jump-peak coordinate to calculate where to display the bonus sprite.
*edit* It might be that the bonus check in this case actually happens when you land (notice that Jumpman moves right after he lands in the .gif above, so the joystick is still being pushed to the right) and it counts the barrels near Jumpman's landing position for the bonus instead of the barrels under him during the jump itself.
