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Keyframing Domain parameters broken: Mantaflow Smoke.
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System Information
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

Blender Version
Broken: version: 2.82 (sub 1), branch: fluid-mantaflow, commit date: 2019-11-26 22:21, hash: rB0ca44974c97f
Worked: (optional)

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)]

Event Timeline

Mark Spink (marks) updated the task description. (Show Details)

I can reproduce that the playhead goes back to frame 1. @Sebastián Barschkis (sebbas), do you know why that happens?

@Mark Spink (marks), I assume you wanted me to create a new fluid system on the domain object? Please, always try to reduce the number of steps we have to do in a few as much as possible.

Mark Spink (marks) added a comment.EditedWed, Jan 15, 2:57 AM

@Jacques Lucke (JacquesLucke) I'm guessing you are/were using the 16 December build to test this, if you read the report 'Broken Version' section, then you will see this has been generated/reported using the 26 November build, as I report a bug where I find it version wise. Therefore the lack of Fluid on all the objects is because you are not using the same build (as in the 16 December build won't 'see' the fluid system modifiers from the 26 November build and vice versa). I just tried the 16 December build and as you found this bug exists with that build as well.

As Mantaflow is rather buggy in quite a few departments, I have somewhat of a busy 'program files' folder-

The one without a suffix being the one which currently runs from my task bar (16 December build), the 'Working' one being the 26th November build (as in i found this T72730 issue with the 16 December build, although this is not a consistent bug I'm afraid- as this bug shows- T73078).
So I use the 26 November build at the current time, if I want to see my results, as I find this renders more reliably as things stand.
If you had used the same build as the bug was reported reported using, the extra steps would not have been needed. I assure you I was NOT trying to make things difficult for you.