Just a quick test with Pidgin 2.6.6 on Ubuntu and SC (latest build). - Ubuntu as well.
1. Audio call from Pidgin to SC: Failed with "ICE error"
2. Audio call from SC to Pidgin - connected, but one sided audio to Pidgin, SC silent
3. Video call from SC to Pidgin - connected, incoming video on Pidgin, sound on Pidgin, silence and no video on SC.
Seems to be an ICE issue: no packets coming in at SC side, but even stranger: no packets going out from Pidgin.
Everything on the same LAN, No NAT involved.
Please have a look at the Log attached. Hope, I could help you improving.
sip-communicator0.log.0 (28.5 KB)