Sorry for the delay. I'm having trouble figuring out what range of values to use for the test. I ran through the following range of values on my Galaxy Nexus so far:
-4.0, -3.5, -3.0, -2.5, -2.0, -1.5, -1.0, -0.5, -0.2, 0.0, 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0
None had any effect on the sort problem with Mario's head:

I did notice something between -0.2 and -0.5 with the waterfall. -0.2 and larger always looks the same with the waterfall drawn on top of everything else:

-0.5 and less always looks the same with the waterfall missing entirely, but other background objects still drawn on top of foreground objects:

What I'm going to look at next is a finer granularity between -0.2 and -0.5 to see how it transitions between those last two images, and then expanding out from the values I've looked at so far.