My mesh set-up is experiencing the problem that looks similar to what Kari is describing, except it is not happening all the time - only after my mesh has been operating for a few days (~10 or so), and the problem is only seen from stations connected to the MAP (when connected directly to RAP all is fine). The built-in MAP to RAP speed test isn't showing any difference to when everything is operating normally - ~450M both ways.
I also don't use RADIUS or change any encryption settings.
The problem appeared after upgrade to 200.5, and can be resolved by rebooting the MAP.
However, couple weeks ago rebooting just the MAP didn't work - had to reboot the RAP as well, and all came back just fine, well, until today when I had to reboot the MAP to make it come to senses again.
In all cases I didn't notice APs shift 5 or 2.4 channels significantly with reboots - I'm guessing they were already on optimal channels, and came back to the same channels after reboot.