writeback-check-output behavior

Hello,

I'm working on a patch to vkms, and I noticed one behavior in the writeback-check-output test that I want to know if it's intended or not.

The test is filling all the pixels of the in_fb, and calculates the CRC expecting the alpha to not change. Even though it's asking for the XRGB plane format.

My question is, is this behavior wrong? or is it deliberated?

Thanks