rtwn connection stops working on CURRENT

Hi,

I'm running into a somewhat weird issue with the rtwn driver
on CURRENT. It usually works for a couple of minutes (if there's
not too much of troughput happening) before the downstream and
upstream rates just "dry up" and the interface stops working.
It happens faster, if there are multiple connections open at the
same time, e.g. having a browser open or fetching mail and doing
a portsnap update.

Once the connection stopped working, dhclient will report the
following:

  Jun 11 12:22:22 athena dhclient[474]: send_packet: no buffer space available
  Jun 11 12:24:08 athena last message repeated 4 times
  ...

wpa_supplicant reports:

  Jun 11 12:22:20 athena wpa_supplicant[335]: wlan0: CTRL-EVENT-DISCONNECTED bssid=... reason=3 locally_generated=1
  Jun 11 12:22:20 athena wpa_supplicant[335]: wlan0: WPA: 4-Way Handshake failed - pre-shared key may be incorrect
  Jun 11 12:22:20 athena wpa_supplicant[335]: wlan0: CTRL-EVENT-SSID-TEMP-DISABLED id=0 ssid="..." auth_failures=8 duration=100 reason=WRONG_KEY
  Jun 11 12:22:20 athena wpa_supplicant[335]: wlan0: CTRL-EVENT-SSID-TEMP-DISABLED id=0 ssid="..." auth_failures=9 duration=152 reason=CONN_FAILED

pciconf -lv:

rtwn0_at_pci0:3:0:0: class=0x028000 card=0x819510ec chip=0x817610ec rev=0x01 hdr=0x00
  vendor     = 'Realtek Semiconductor Co., Ltd.'
  device     = 'RTL8188CE 802.11b/g/n WiFi Adapter'
  class      = network

An pointers on tracking this issue down and getting it fixed are
highly appreciated.

Cheers
Marcus