elk.mrtree edges behave weird with identical labels in different child nodes

[YorikHansen]

Describe the bug
When child nodes have identical labels, the edges are not properly layouted. This includes:

1. edges starting from the east side of the node even though they should start on the south,
2. outgoing edges not being justified properly and
3. incoming edges that enter a node in an unexpected angle.

See an example

Expected behavior
The tree is drawn in the same way it would be if the labels weren't identical or not existing at all.

Screenshots

ELK Version
0.9.1 (and all other versions) and the current snapshot.

Additional context
Add any other context about the problem here.

[soerendomroes]

It seems to depend on the actual labels in there. Interestingly this works.

[soerendomroes]

Here is a smaller example.

[YorikHansen]

It seems to have nothing to do with the length of the label but with the fact that they are identical for both children. This example with long node labels is also affected.

Therefore I changed the title and description of the issue