ath9k roaming for no obvious reason

I've been seeing this for a couple of months now, and updating to the latest wireless-testing git hasn't improved things:

Apr 20 07:31:12 violino NetworkManager: <debug> [1240237872.002673] periodic_update(): Roamed from BSSID 00:12:17:26:56:10 (HighlandSun) to (none) ((none))
Apr 20 07:31:18 violino NetworkManager: <debug> [1240237878.004208] periodic_update(): Roamed from BSSID (none) ((none)) to 00:12:17:26:56:10 (HighlandSun)
Apr 20 07:32:12 violino NetworkManager: <debug> [1240237932.003138] periodic_update(): Roamed from BSSID 00:12:17:26:56:10 (HighlandSun) to (none) ((none))
Apr 20 07:32:18 violino NetworkManager: <debug> [1240237938.004280] periodic_update(): Roamed from BSSID (none) ((none)) to 00:12:17:26:56:10 (HighlandSun)

<<<

This is on an HP dv5z laptop, lspci shows
08:00.0 Network controller: Atheros Communications Inc. AR928X Wireless Network Adapter (PCI-Express) (rev 01)

It's about 10 feet from a Linksys WRT54G and there's nothing blocking the line of sight. I'm running a 2.6.29.1 kernel at the moment; used the compat-wireless git to build the wireless stack.

At random intervals (15-20 minutes or so) it loses the association completely and NetworkManager asks me to re-authenticate. This behavior seems to have gotten worse in the current snapshot. Has anyone else seen this, any ideas?

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