An API call to wbeditentity, that uses the existing claim guid, is able to change the property of the claim.
See
https://www.wikidata.org/w/index.php?title=Q6240488&diff=114789738&oldid=114788831
In the diff, the presentation assumes the property of the claim is the same before and after.
However in the previous revision, there was a 'title' claim. In the modified revision, there is a 'birth name' claim.
Either the API or the Diff logic is wrong.
Version: unspecified
Severity: critical
Whiteboard: u=dev c=backend p=5 s=2014-04-01