Comment 7 for bug 1048657

I had the same GTK_IS_TREE_MODEL message in 2.6 (i don't remember gimp_wire_read being part of my problem)
in 2.8 I had "gimp-2.8 crashed with SIGSEGV in completion_match_func"
both were immediately after Save As (2.6) or Export As (2.8) a PNG input file as a PNG (with a new name)

It seems that my issue may have been related to my Xauthority system. For some reason, my login screen had been replaced with gdm and lightdm, although installed, was not default. Reinstalling lightdm and reconfiguring it while wiping out my .Xauthority file seems to have cured my woes. Now 2.8 works like a charm.

Before I cleared out my /home/username/.Xauthority I had some problems logging in as my default user, so you may want to have a spare account to log into.