May be a wrong power management setting/code leads to ignoring of input events. I saw similar issue in some other boards.
If I am not mistaken, the primary difference on the newer, QSB-R board is the use of a Freescale MC34708 Power Management Integrated Circuit (vs. a Dialog DA9053 PMIC on the older QSB board).
Not sure about the issue. But, Quick work-around to unlock, try to send a key event from Serial or ADB port,
$ input keyevent 82