I use an external wifi adapter. I also use backtrack in a virtual machine, but I don't think that's the issue.
Basically, when I unplug the modem (usually accidentally), linux will often freeze. This was NOT a problem with BT4 R1. I've also tested this with two different virtual machines (Desktop Parallels and VirtualBox) to no avail.
If I remove the rtl8187 module before unplugging the adapter it doesn't freeze. I would test the r8187 driver but the r8187-driver package doesn't appear to install it (another bug).
Removing the rtl8187 module is NOT a solution because the modem cable often disconnects unintentionally. When this happens I have to reboot BT5 and start over.
Since this is a freeze and not a crash, I have no backtrace to report.
The only work-around I know thus far is to use the ancient BT4 which has the old rtl8187 which is far inferior in terms of both power and sensitivity (for whatever reason).