I think it is the checklist. When creating a new segmentation based on a dynamic image you now can decide between a static segmentation that has a single timestep spanning over all reference image timesteps and a dynamic segmentation to have matching timesteps. In the latter case only the current timestep should be affected except the tool is explicitly giving the option to be applied to all timesteps at once. Can you confirm?

That's exactly what I wrote and defined in the checklist. The checklist is correct as it perfectly reflects what's happening in the workbench. This is - as described in the title of the corresponding section - valid for 4D test data.

Edit:
If you recommend this we could add an instruction to test both checkboxes. Please state so in the mentioned task. This was just recently added with D450.

To be honest, I just did not understand the checklist correctly. If you know the outcome and read the checklists, they are fine. But for me, it was like a new test starting with loading and testing 3D Data again. So I misunderstood the line Bei den folgenden Aktionen stets mehrere Label, auch auf unterschiedlichen Layern testen. as beeing a new test, because it had of kind of title character. And that is why I thought, I would start with a 3d Image again...

If you have suggestions for a better structure, please feel free to add it to T28130. The checklists were not even existing before and my goal was to overhaul all the (multi-)label segmentation checklists to include 4D-data tests. I also strove for consistency throughout all checklists.
I see that the bold written statement reads as a new test - that could be changed. However, the test right before already dealt with 4D image data (4D Bild als Testdatensatz) so I assumed it was clear that the 3D-data tests were already finished.
I will also think about some rephrasing / different text format.