xapian-check sorted order error

Hi,

We were running xapian-check on one of our Xapian indexes and it
returns the following error:

position:
baseB blocksize=8K items=809896869 lastblock=2090419 revision=3161
levels=3 root=2084903
Failed to check B-tree: DatabaseError: Items not in sorted order

The other tables verify without issue. It looks like our oldest backup
of this database (a month old) has the same issue. Searching and
indexing are still working fine as far as we can see.

Running xapian-check with the F option to "attempt to fix a broken
database" doesn't seem to have any effect - the position table still
reports the same error both during the run with F enabled and on
subsequent runs.

Is this something we need to worry about? Can it be resolved? Thanks.

ATB,
Matthew