Went to reproduce #539 and was messing with trades.
If you’re in a group chat, lets say for http://steamcommunity.com/games/221410 and click the large dropdown, and do ‘invite to trade’, you get this:

userfriends.cpp (2882) : Assertion Failed: Bad steamID [c:1:4178173] passed into CUserFriends::GetClFriendBySteamID()

Assert( Assertion Failed: Bad steamID [c:1:4178173] passed into CUserFriends::GetClFriendBySteamID()
 ):/home/buildbot/buildslave_steam/steam_rel_client_ubuntu12_linux/build/src/clientdll/userfriends.cpp:2882

Installing breakpad exception handler for appid(steam)/version(1357686090_client)
Uploading dump (in-process) [proxy '']
/tmp/dumps/assert_20130110001345_4.dmp
success = yes
response:  CrashID=bp-acef8196-7014-4528-a34e-389e62130109
userfriends.cpp (1452) : Assertion Failed: steamID.BIndividualAccount()
Assert( Assertion Failed: steamID.BIndividualAccount() ):/home/buildbot/buildslave_steam/steam_rel_client_ubuntu12_linux/build/src/clientdll/userfriends.cpp:1452

Installing breakpad exception handler for appid(steam)/version(1357686090_client)
Uploading dump (in-process) [proxy '']
/tmp/dumps/assert_20130110001425_5.dmp
success = yes
response:  CrashID=bp-f54ffe96-10c1-4289-928a-d42b82130109
userfriends.cpp (1452) : Assertion Failed: steamID.BIndividualAccount()