Thanks for the report. I don't know offhand about WORDS_BIGENDIAN.
The IMAGE_INSTANCE_GTK_MASK issue is a known bug, fixed in the Mercurial
repo, AFAIK. hg tip has many other fixes not in 2.5.28, so upgrading is
highly recommended. Testing would be very much appreciated!
Note that GTK is currently not a high priority for us (our main man on
GTK went and got a life, he's still around but not so active here), so
response may be slow. Keep the bug reports coming and we'll probably
upgrade its importance.
Any help with porting to GTK+ v2 would be really really appreciated.