I had an older installation of MigxDb that I hadn’t added items to for quiet some time. When I added new items it wouldn’t save strings - just integers and boolean objects. (I am running Modx 2.8.1 - but I am not sure when the problem started.)
The problem was in the schema, the old files didn’t have the phptype.
To fix the problem I updated the schema file and edited the “<package_name>.map.inc.php” adding ‘phptype’ => ‘string’, to each of the arrays with a ‘dbtype’ => ‘varchar’, (Don’t forget the trailing comma)