Just wanted to post the resolution in case anyone else runs in to the same problem.
In fop2.cfg I had specified 'buttonfile=buttons.cfg' to use my hand-edited button file, and was using #exec autoconfig-users-freepbx.sh to automatically generate the users. The autoconfig-users-freepbx.sh script also contains an exec to generate a button file. I commented out the exec line in autoconfig-users-freepbx.sh, and now it is working as expected.
