Same issue here. Pressing the button triggers a keyboard lock and no longer a password lock.
It strated after I upgraded to the latest OS from 4.6.x
From what I read on other forums, looks like it might be an OS bug unless it is a deliberate choice given that most users do not password protect their BBs.
8120 BIS 220.127.116.11
9700 BES 18.104.22.1686