i noticed that if phone is locked and you plug in usb cable to charge your phone charging wont kick in till you press power and slide your finger to unlock it.
IF you take too long to unlock and the usb storage or pc sync options are gone from the screen n900 wont be charging.
it seem random at times where even when locked it still kicks in on its own and also the choice usb storage / pc sync doesn't fade away even after longer time, could be related to how i locked the phone, where it acts differently if it locks itself on its own after idle time and differently if you lock it by slider or power button
clearly software bug but can't find 100% way to reproduce it yet.
hope someone will