Actually, there are at least three bug reports on this same problem on launchpad:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1144322
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1165433
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1189998
Actually, there are at least three bug reports on this same problem on launchpad:
https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/1144322
https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/1165433
https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/1189998