Single channel JPEG files are stored in 4 channels image buffers, with their
bit planes set to 8.
When creating the GPU texture the number of bit planes is used to identify
if the data could be stored as a single channel texture, but in this case
the source data contains 4 channels and doesn't align with the GPU
texture format.
In Blender 3.6 the way how bit planes were stored changed (the planes
used to be 32 for the grayscale byte images matching the number of channels,
but now is set to 8, matching the original loaded image).
Since Blender 3.5 the grayscale byte images are uploaded using a single channel
GPU format, which leads to the mentioned artifacts. Grayscale byte buffers never
seems to have worked since its introduction in
https://archive.blender.org/developer/D15484
This PR disables using the grayscale GPU textures when it sourced from
a byte image.
Pull Request: https://projects.blender.org/blender/blender/pulls/114441
2193bd4b89