After applying this patch, I have not had any problems so far.
My case is using two MT6000's as dumb AP's, no fast roaming configured.
On that AP, with WED enabled and bridger running, I had the same problem as in the thread above.
Interestingly, when WED is disabled, there are no roaming related problems.
The relevant issue seems to be resolved, but I plan to operate with WED disabled because enabling WED in dump AP makes the latency worse.