System Information
Operating system: Linux-5.4.0-7634-generic-x86_64-with-debian-bullseye-sid 64 Bits
Graphics card: Radeon Vega Frontier Edition (VEGA10, DRM 3.35.0, 5.4.0-7634-generic, LLVM 10.0.0) X.Org 4.6 (Core Profile) Mesa 20.0.8

Blender Version
Broken: version: 2.90.0 Alpha, rB02c09773ea07

I checked if rB2840782d8478 is the culprit, but it didn't work with its parent commit either (the one mentioned above).

Worked: 2.83

Short description of error

Background is drawn with no alpha for some animation channels.

Exact steps for others to reproduce the error

• Insert keyframe for default cube
• Enter Animation workspace

-> Icon for the cube should have a black background in the Dope Sheet channel list.