First things...
1) What version of WiNG on the AP650's? versus, what version of WiNG on the 7522's?
2) Did you replicate the AP650 profile for the AP7522's?
3) Same SmartRF policy used for both 650's and 7522's?
4) Same WLAN Profile used for both the 650's and 7522's?
5) Are you 100% certain this problem only started once you began using the 7522's? Could it just be coincidental timing?
If you see a pattern here, we're looking for anything that is different except the AP hardware.
Once you can eliminate any possible configuration differences, then we can start investigating if there might be something at fault that is specific to the 7522, that did NOT exist on the 650.
For those users affected, *how often* does it happen?
Any idea if this client-side problem is affecting ALL users or just some subset?
Possible to take one of the affected units and upgrade its firmware (if there is an update) and then see if it continues to have an issue?