At least for me, this bug is fixed with version 2.6.15-8 (backports.org:
2.6.15-7bpo1). It is also mentioned in the changelog:
linux-2.6 (2.6.15-8) unstable; urgency=high
[ maximilian attems ]
* Add stable Release 2.6.15.5:
[...]
- Address autoconfiguration does not work after device down/up cycle
Cheers
Harry