After enabling CUPS and adding a printer via the GNOME control panel, a dialog pops up that says "scanning for drivers". I hit cancel and it popped up again, and when it completed, the first one appeared to still be running, so there was an additional "scanning for drivers" dialog open. Killing this process removed the dialog:

/usr/bin/python2.7 /usr/share/system-config-printer/scp-dbus-service.py

The printer was successfully added even though this quirk occurred.