Ah, I can re-create it if I disable another layer in Simple Servers QC comp. I see the issue. It has to do with how jitter clears the back-buffer.
Jitter defaults to a erase color of 0, 0, 0, 1. If you clear with 0, 0, 0, 0, it looks correct. This has to do with the blend mode math, default being over, aka 6, 7.
Since the erase color alpha component is 1, not 0, it looks different from every other app. Most applications do not do a clear the same way jitter does, as far as I can tell. (Erasing to 0, 0, 0, 0 does not leave artifacts like it does in Jitter in any other app).