Solved by a Lenovo BIOS upgrade which is now available for X61t machines as well. See here: http://www-307.ibm.com/pc/support/site.wss/document.do?sitestyle=lenovo&lndocid=MIGR-68005 The following changelog line is relevant to this bug:
Version 7SET23WW (1.09) * (Fix) Unexpected interrupts from the USB controller may occur. (BIOS) -- kernel disables irq after 10 minutes https://bugs.launchpad.net/bugs/126369 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs