When manually switching between system address book and one other address book with "search.py -a", syncevo-dbus-server crashed inside folks. Need to investigate.
Could not reproduce the crash. What I found and fixed instead is Folks bug https://bugzilla.gnome.org/show_bug.cgi?id=689146 - disabling address books had no effect.
There's an automated test now which covers enabling/disabling databases: TestContacts.testActive.