OK, I think this is might a bug, but need to check with Kovid. At minimum, the Android driver needs another configuration entry.
Details: The problem is two-fold. First, that card name (PROD_SGH-T849_CARD) is not known to the Android driver, but the main memory name (PROD_SGH-T849) is. Second, the 'name' of main memory is a prefix of the name of the SD card, so the drive existence test seems to match both. Because both match, it takes the last one, which is the SD card.