Reproduction steps:
1. Open the attached project
2. Enter Play mode

Result:
The cube on the left uses Graphics.Blit() which DOES NOT ignore the depthSlice parameter, hence the cube is rendered correctly
The cube on the right used CommandBuffer.Blit() which DOES ignores the set depthSlice parameter, therefore it only renders to the first depthSlice

Reproducible on: 5.6.0b1, 5.6.0b8

Couldn't reproduce on an earlier version, because Unity crashes on entering Play mode

Tested on Windows 10