Irfanview (Image viewer) slow when WB running

Irfanview, a great image viewer program for Windows, for some reason, is much slower when a WindowBlinds skin is active. Scrolling and loading images takes longer than it should.

I did add it to the program exceptions, so that it doesn't skin the program, but there are still slowdowns, just not as bad.

It's freeware and I know it's a bit of a pain to install that to do testing, but please could you have a look and see what the problem is? I've posted on their forums as well, not sure who's program fault it is, or maybe it's just a clash. Thanks!