Surface2 has a non-standard Wintab ID on

const uint cursorTypeBitMask = 0x0F06; // bitmask to find the specific cursor type (see Wacom FAQ)

if (((csr_type & 0x0006) == 0x0002) && ((csr_type & cursorTypeBitMask) != 0x0902)) {
    tdd.currentDevice = QTabletEvent::Stylus;
} else if (csr_type == 0x4020) { // Surface Pro 2 tablet device
    tdd.currentDevice = QTabletEvent::Stylus;
} else {
...
}