Touch screen input only uses cursor coordinates

I have a ViewSonic touch screen display connected to an Android PC (kernel 3.0.36+) via HDMI & USB. The display shows everything correctly. Furthermore, the Linux kernel recognizes it.

dmesg:

<6>[   99.699034] usb 2-1.2.3: new full speed USB device number 8 using usb20_host
<6>[   99.800896] usb 2-1.2.3: New USB device found, idVendor=0408, idProduct=3008
<6>[   99.800993] usb 2-1.2.3: New USB device strings: Mfr=1, Product=2, SerialNumber=4
<6>[   99.801099] usb 2-1.2.3: Product: OpticalTouchScreen
<6>[   99.801169] usb 2-1.2.3: Manufacturer: Quanta
<6>[   99.801226] usb 2-1.2.3: SerialNumber: 0000
<4>[   99.805402] quirks: 0x00000000

The problem is that the screen, while I can touch anywhere, only registers the tap at the curser (wireless keyboard/mouse connected) location. If I move the cursor and tap anywhere on the screen, the new location receives the tap. If I remove the keyboard/mouse dongle the behavior remains, but now I can't move the cursor.

Does anyone have any ideas what might be going on here?