Unexpected request status/Cannot have more than one request with the same position in the queue

This bug has been hard to replicate. I did record a [screencast of it](https://youtu.be/fETAUsDa_NM) (though it is not the most tidy presentation ever) – and I have a [longer recording](https://youtu.be/K_uogSqVtok) which includes 4 minutes of possibly irrelevant muddling around, but is where I created the initial requests.

NOTE: There are some repro steps to check and test in CHAL-49, as well

I am in the BugFest q3.2 environment, and logged in as mwalter.

As best as I can make out, these are the important things I did:

Steps:
Create two requests under item A.
Create four requests under item B (same instance).
Check in both items so that they are placed in transit.
It will be impossible now to move either request in position 1.
Move the request on item A in position 2 to item B.

This is where I got the error described above.

I have also seen this wording in a JSON modal format (see screenshots), but I have not been able to replicate that under controlled circumstances.