I can reproduce this with Collabora's Freeswitch server and it eats all my battery and loads of bandwidth. So this is kind of critical. Freeswitch side bug: http://jira.freeswitch.org/browse/FS-678 But from the log (I didn't investigate further), it looks like a bug in tp-ssip. I've only tested with the version that is on the N900 which means sofiasip 1.12.10-0maemo5 and tp-ssip 0.6.2-0maemo4 I'm not sure how to reproduce it reliably..
This is in fact a sofia-sip bug.
A fix can be tested using this branch: http://gitorious.org/~mzabaluev/sofia-sip/mzabaluev-sofia-sip/commits/fix-ob-contacts
The fix is merged into sofia-sip master head.
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