"DivX 3.11 Post processing 10" - a bug?

I'm using "Increase/decrease postprocessing" hostkeys very often. When I'm decreasing pp level for DivX 3.11 codec, it seem to wrap below zero.

I.e.: let current pp level is 1. I hit F7 (decrease pp) - BSPlayer shows "DivX 3.11 post processing level 0", which is ok. I hit F7 again - BSP shows "postprocessing level 10". F7 once again - "postprocessing level 9". Now BSP is "locked" between level 9 and 10, when I'm pressing F8 to increase pp BSP cab switched from 9 to 10 (and backward) but not further. No effects on image, too.

It this a feature which I cannot understand or just a bug?