I'm having the same problem. 

I do NOT have system-ca-certs in the NetworkManager connection file. I turned off power saving and ipv6. Still get 

Dec 19 23:57:06 desktop kernel: [  110.811108] wlan0: send auth to 00:19:cb:58:f6:b9 (try 1/3)                                                                              
Dec 19 23:57:06 desktop kernel: [  110.813360] wlan0: authenticated                                                                                                         
Dec 19 23:57:06 desktop kernel: [  110.813531] rt2800usb 2-1.5:1.0 wlan0: disabling HT as WMM/QoS is not supported by the AP                                                
Dec 19 23:57:06 desktop kernel: [  110.813536] rt2800usb 2-1.5:1.0 wlan0: disabling VHT as WMM/QoS is not supported by the AP                                               
Dec 19 23:57:06 desktop kernel: [  110.813718] wlan0: associate with 00:19:cb:58:f6:b9 (try 1/3)                                                                            
Dec 19 23:57:06 desktop NetworkManager[935]: <info> (wlan0): supplicant interface state: authenticating -> associating                                                      
Dec 19 23:57:06 desktop kernel: [  110.829841] wlan0: RX AssocResp from 00:19:cb:58:f6:b9 (capab=0x411 status=0 aid=3)                                                      
Dec 19 23:57:06 desktop wpa_supplicant[1348]: wlan0: Associated with 00:19:cb:58:f6:b9                                                                                      
Dec 19 23:57:06 desktop kernel: [  110.836913] wlan0: associated                                                                                                            
Dec 19 23:57:06 desktop kernel: [  110.836925] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready                                                                     
Dec 19 23:57:06 desktop NetworkManager[935]: <info> (wlan0): supplicant interface state: associating -> associated
Dec 19 23:57:07 desktop avahi-daemon[944]: Joining mDNS multicast group on interface wlan0.IPv6 with address fe80::f27d:68ff:fe15:5756.
Dec 19 23:57:07 desktop avahi-daemon[944]: New relevant interface wlan0.IPv6 for mDNS.
Dec 19 23:57:07 desktop avahi-daemon[944]: Registering new address record for fe80::f27d:68ff:fe15:5756 on wlan0.*.
Dec 19 23:57:11 desktop wpa_supplicant[1348]: wlan0: CTRL-EVENT-DISCONNECTED bssid=00:19:cb:58:f6:b9 reason=4
Dec 19 23:57:11 desktop kernel: [  115.755373] cfg80211: Calling CRDA to update world regulatory domain
Dec 19 23:57:11 desktop kernel: [  115.758863] cfg80211: World regulatory domain updated:
Dec 19 23:57:11 desktop kernel: [  115.758867] cfg80211:   (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp)
Dec 19 23:57:11 desktop kernel: [  115.758869] cfg80211:   (2402000 KHz - 2472000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
Dec 19 23:57:11 desktop kernel: [  115.758872] cfg80211:   (2457000 KHz - 2482000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
Dec 19 23:57:11 desktop kernel: [  115.758874] cfg80211:   (2474000 KHz - 2494000 KHz @ 20000 KHz), (300 mBi, 2000 mBm)
Dec 19 23:57:11 desktop kernel: [  115.758876] cfg80211:   (5170000 KHz - 5250000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
Dec 19 23:57:11 desktop kernel: [  115.758878] cfg80211:   (5735000 KHz - 5835000 KHz @ 40000 KHz), (300 mBi, 2000 mBm)
Dec 19 23:57:11 desktop NetworkManager[935]: <info> (wlan0): supplicant interface state: associated -> disconnected

Needless to say, it used to work and all other devices still work, only 13.04 has issues.