Tree merge is broken

[aaannndddyyy]

I have a tree A of some two hundred persons and another tree B of around 20.
Both trees have one person in common.

I tap on the three dots next to B and select merge tree. I then select tree A and click next.
I'm asked about the one person and I say yes. Then I'm asked again about the same person in other pairings - which is ok, as it gives s tiny consistency check - where I always press no. All other questions are no, because no other person is shared between both trees.

Merging both trees into a new one and opening the new one I see that my niece jas become my grandmother, in addition to being my niece and the tree goes up seemingly to infinity.

Tree B, the smaller one, contains only a second partner

[aaannndddyyy]

I have repeatedly done that procedure and always get that result, so it was not a glitch .
Interestingly, if I merge starting from tree A instead of tree B, it seems to work fine. The result looks as expected and I haven't found any errors so far.

[michelesalvador]

It's hard for me to say what's happening here without seeing the actual trees.
Could you please post the two trees or some equivalent to reproduce the issue?

[aaannndddyyy]

I'll see if I can post them.
Meanwhile, another issue with merged trees has popped up:
I merge two tress with approx. 50% people in common. One tree contains photos , the other not.
The result is a new tree. It looks good. All persons are shown correctly , all photos match.
I zip-export (backup) the tree and reimport it, it still looks good .
I send that zip to a friend, he opens it, and the tree itself is correct, but some photos are associated with the wrong persons: tree root person A has two brothers: one brother shows A's photo, the other brother shows the photo of A's wife .
Probably to to with reindexing (IDs) during the merge. Something is different on the system where the merge Wass performed, and a remote system .