I recently upgraded an AP from another OS/SBC solution to a RB500 with 2.9. With both SBC's, I used a Senao/Prism 200mw minipci 802.11b card for the AP. I had one Atheros card in the other solution for the backhaul and two Atheros cards in the RB500 for backhaul.
After upgrading to the RB500, I experienced significant problems with the AP clients being able to connect consistently. Some clients, which had as low as a -57db connection strength with the other solution could not connect at all. Some clients would connect initially, then disconnect until I rebooted the RB500. Finally, after a number of days of problems, and then losing wireless connectivity totally by trying to switch to the legacy wireless drivers (see my post(s) in the Routerboard section), I switched back to the other solution, and my problems went away. All clients are now connected and working properly.
A number of months ago, I tried upgrading another AP running MT 2.8 with Prism cards to a 2.9 beta, and seemed to experience the same problem. I had hoped that the problem had been resolved in the updated 2.9 version, but it has not.
Has anyone else experienced this problem? Is there a solution that I have not discovered? Do I just need to use Atheros cards exclusively in 2.9?