I've actually had this issue as well. As a beta tester, I'd normally report this but it's a random thing that I haven't been able to reproduce.
What I think it MAY be, is something to do with old wah sounds in the new wah block. I've since updated my old wah presets using the new wah block settings and resaved my sounds. I've not experienced this since, so it *may* have something to do with it.
Rich, try this for me. Resave one of your presets next to an old preset that hasn't been edited with new wah settings. While saving new wah settings, make sure the wah block is not engaged prior to saving if you use auto on. (Like the others have mentioned)
Try changing through presets and see if it happens with the new preset you just created and of course try switching into the old.one as well.
I'm going to do the same on this end to see if I come up with anything. If we both have the same results, I'll mention something to the guys that can make a difference in the bug department. Let's give it a few days and report any issues.
Anyone else experiencing this can jump on in as well. But in my experience, redoing my wah block and resetting it (just like we do amps with new firmware, cycle through the different wah's to load the new settings) stopped this from happening on my end. Could have been coincidence of course.
I have about 20 presets I haven't updated yet, so they will be a good test for this to see if it may be the issue. Again this is just a test and isn't a real bug at this time...but is worth looking into further. I'll report back anything I find out.