ERROR: permission denied to finish prepared transaction

I'm seeing a bunch of these error messages:
Feb 16 12:04:51 QA-HC01-DB01 postgres-hc01[26420]: [2-1] user=xy,db=x,pid=26420 ERROR: permission denied to finish prepared transaction
Feb 16 12:04:51 QA-HC01-DB01 postgres-hc01[26420]: [2-2] user=xy,db=x,pid=26420 HINT: Must be superuser or the user that prepared the
transaction.
Feb 16 12:04:51 QA-HC01-DB01 postgres-hc01[26420]: [2-3] user=xy,db=x,pid=26420 STATEMENT: ROLLBACK PREPARED
Feb 16 12:04:51 QA-HC01-DB01 postgres-hc01[26420]: [2-4]
'1197822575_uwQAAAAAAABHVE1JRAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==_AQAAAAAAAABHVE1JRAAAAAAAAA
Feb 16 12:04:51 QA-HC01-DB01 postgres-hc01[26420]: [2-5] AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=='

As far as I can tell, that means that user xy is trying to rollback a prepared TX that it didn't create.
is that the only reason this error would show up?

I'm asking becase, as far as I can tell, xy is the only user on the box that would be doing prepared tx's

this is 8.3

Thanks

Dave