ASUS Response: We've received a response from ASUS that they're unable to replicate the problem on production units (I/O units are, technically, pre-production), so this may have been sorted out in time for the initial consumer run. It appears, then, that this problem is at least affecting only some units.

Some have suggested this is a native behavior with IPS displays called "image retention." I did a side-by-side of the same image with a Transformer Prime and Trasformer Pad 300 - both of which have IPS displays.