Tree merge is broken about familygem HOT 3 OPEN

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.

from familygem.

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?

from familygem.

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 .

from familygem.