I think I've resolved the issue for myself, but I don't have a good understanding of what I did to to fix it...
I downgraded libgdk-pixbuf2.0-0 to 2.26.1 and satisfied it's dependencies. Then gnucash and gmpc began to work. As I'm a gluten for punishment, I then ran apt-get upgrade and let it upgrade libgdk-pixbuf2.0-0 and it's dependencies back to 2.28.1. After doing this gnucash continues to work even after a full restart. I'm not really certain whats going on, but I do feel confident in saying this was caused by user (my) error. Feel free to close this bug. Thanks -- DavidT -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org