System Information
Operating system: Linux-5.3.0-59-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: AMD Radeon (TM) Pro WX 7100 Graphics ATI Technologies Inc. 4.5.13581 Core Profile Context FireGL

Blender Version
Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-06-23 17:20, hash: rB11a390e85e2b
Worked: (newest version of Blender that worked as expected)

Short description of error
In the sequence editor the playhead is rendered twice.

Exact steps for others to reproduce the error
Go to sequencer and press play. Introduced by {cc3e808ab47887c002faaa8a28318a2b4f47e02a}