Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.86
Broken: version: 2.82 (sub 1), branch: fluid-mantaflow, commit date: 2019-11-26 22:21, hash: rB0ca44974c97f
Short description of error
Keyframes on domain parameters, Timescale, Density, etc. can't be edited except on frame one (or whatever the first frame is) once a keyframe has been set, if you enter a value at say frame 5, when you hit enter the timeline playhead goes back to frame 1 (or start frame), so any keyframe set which is not on the first frame can't be changed value wise, unless you use the Graph Editor.]
Exact steps for others to reproduce the error
[Set a value on frame 5 (for example) for any parameter which can be keyframed in the Domain object Physics panel, and hit enter- the playhead will go back to the first frame.
Then set a keyframe on frame 5 (using 'i' over the value slot), and then try to change the value of that keyframe in the Domain Physics panel- bingo!
If you want to change the value you have to use the Graph Editor.
Now try the same thing in the Soft Body Physics panel for the SoftCube object, or in the Fluid panel for the Emitter object, you can change the values in these panels without the playhead going back to the first frame.
I'm pretty sure this is a Mantaflow feature to make sure the bake begins from the first frame, it's just not been fully thought through, as in it makes keyframing & adjusting those keyframes a pain for Domains in Mantaflow.
Try with this-
I just tried the above in the 'old' smoke sim, in Blender 2.81a release version, and this works as expected, as in the playhead does not go back to the first frame when you press enter after entering a value in the Domain Physics panel, so you can change keyframe values without using the Graph Editor.]
[Based on the default startup or an attached .blend file (as simple as possible)]