Nonof Youbuis

can confirm for 1.17.1 too and I think I found another symptom/manifestation of the same bug (water source from waterlogged stair influenced and influencing water/blocks around it even when it shouldn't). -> MC-239475

can confirm in 1.17.1 and added another example:

(the orange blocks are normal solid blocks and the fences on top are all waterlogged and blocked with sings.)

Oh and it doesn't look at all like never fixing these old issues didn't create any new problems later on.... (<- be aware of the sarcasm! And I'm not sure if the amount of negations is right in there)

-> MC-239475, MC-228434 and more...

can confirm it in 1.17.1 too and added a slightly less visible example where the water isn't showing a flow animation. It just gets a slope/angle instead of being flat.

And I think I stumbled over another symptom/manifestation of the same bug -> MC-239475

@Felix Huang - how did you get to that conclusion?
I'm pretty sure it's not lag or a server issue because the bug is predictable repeatable. Did you even try to replicate it? (Why post your assumption without any testing?)

I noticed it on my server (spigot), replicated it there and then tested different orientations in creative mode locally without any server (and no lag I'm sure) and to make that screenshot.

It's even dynamically testable by placing blocks under the floating stairs after two were already waterlogged.
Depending on the placed blocks it suddenly behaves as it's supposed to (first only on dry stair gets wet, then the other).

And how is lag supposed to lead to the screenshot I attached? Exactly the same lag at exactly the right moments when I placed water but only in two of the four different examples?