distortion when routing dspB 1/2 -> dspA 7/8

I've come across a strange problem with my H8000FW. In a very basic test routing setup, I'm getting a kind of digital distortion much like a bitcrusher sample-rate reduction effect. Here is the test case: set both DSP A and B to the "thru" preset (#12) and then set the routing as per the first screenshot i've attached here:

Playing a signal from the FW 1/2 in from my PC ends up with an ugly output!

Now, when I route things differently, it goes away. This second image is virtually the exact same setup, but does not produce the distortion:

All I've done is move the DSP B OUT 1/2 to the A IN 3/4 instead of A IN 7/8. This is consistently reproducible, although yes, it's odd to route low-numbered outputs from DSP B to high-numbered inputs on DSP A (I was doing this because I was building a patch where I wanted to use DSP B as an "insert" on the DSP A signal flow).

p.s. if you can't see the whole image here you may need to right click and choose one of the menu options to show the image alone in a new page.

Thanks!

Josh Whiting