Mike,
My signal bar displays the following: G for GPRS, E for Edge, 4G for HSPA+ (single and dual, even while idling), and 4G LTE for the obvious (even while idling as well). I agree that it is weird to display UMTS while it says 4G since my old phone used to say 3G for UMTS and H+ for HSPA+.
I'm going to going to a T-Mobile store tonight (contingent on leaving work on time) to force a Samsung to DC-HSPA+ to see what your app displays. Fingers crossed!