Undo diffget in vimdiff

Question

Say I have a merge conflict in Git, and try to resolve it with vimdiff using diff3 view. Here is a screenshot:

Now while resolving, I want to diffget once from LO see how it looks like, undo, and then diffget from RE. Another situation is that I have diffgeted from the wrong place, say LO, so I want to undo and diffget the correct one, say RE.

So first of all I do :diffget LO and get what is expected:

So far everything is ok, but now I want to undo the last diffget, to diffget from RE. So I undo with u and get to what I had before (though, note the highlighting difference):

And now simply diffget from RE:

So I got one additional redundant octocat line diffgeted from RE.

Below is what I was expecting:

        +----------+------------+
        |  actual  |  expected  |
        +----------+------------+
        |    cat   |    cat     |
        |    dog   |    dog     |
   ??   |  octodog |   octodog  |
  ----> |  octocat |   octocat  |
        |  octocat |            |
        +----------+------------+

So my question is, why is this happening? And how can I achieve the behaviour I expected?

Answer 1

(cf discussion)

It seems that at some point, running the diffupdate command solves the problem.

:diffupdate updates the current diff view. It changes the diff colors to match the new state between files. It also update the folds, that are displayed to keep the diff buffer relatively small.