It seems that the device class is reset to 0x580000 when the bluetooth is switched of and on, regardless of the connetion to the PCSuite. However, the triggering event for this problem still seems to be related to the first time I connected to the PCSuite using bluetooth, because I do remember that Windows correctly identified the N900 as a bluetooth phone on that first time. I've read a bug regarding firmware issues in some bluetooth chips of N900. Does anybody know anything about this? Could you check the device class of your N900 by issuing the command "hciconfig hci0 class" in the console?
Indeed, I'm not sure about being PCSuite who altered my N900 the first time I connected it using bluetooth. It could also be Windows 7 x64, but it seems less probable.

Cheers!