CDMA auto (PRL), go to the regular System Settings, More..., Mobile Networks.
That's it, just viewing that screen causes it to persist somehow.
Probably because it reads the setting to show "Prefered network mode: CDMA only" and then writes it somewhere.
EDIT: Also, long ago I made a review about this on the app's market page, please find it and mark as helpful if you can. (It's now listed as by "A Google User")