The error can be reproduced in the following way:
- First, create some nodes, and persist.
- Then, move a node after another one, filling the LAST free sorting index between the nodes. Do NOT persist after that.
- After that, try to *again* move a node to this spot. In this case, we need to *renumber*
the node indices, and the system needs to take the before-moved node into account as well.
The bug tested by this testcase led to wrong orderings on the floworg website in
the documentation part under some circumstances.