Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 399.24
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e
Short description of error
The blue timeline that displays the keyframes when animating a mask in the image viewer > mask mode is hidden when the header sits at the bottom of the window. It is only visible when A: the mask shape is 'G' selected or B: the 'flip to top' header option is selected.
Exact steps for others to reproduce the error
-Open image viewer in blender
-Switch mode to mask mode
-Create a shape for animating
-If the image view header is set to sit on the bottom of the window, the blue timeline is only visible when the shape is 'G' selected.
-To see the timeline and keys at all times, the header must be moved to the top of the window.
[Based on the default startup or an attached .blend file (as simple as possible)]