Failed integrity check during merge

Thu Sep 20 08:54:44 UTC 2012

I was surprised today a little bit. One of my coworkers tried to make
a merge from
default to feature branch and got

abort: integrity check failed on data/SomeDir/SomeFile.mdb.i:1!
[command returned code 255 Wed Sep 19 13:54:43 2012]

File is a big binary blob (~4 Mb) so my warning sign started to blink.
We tried hg verify and all looked OK. Then we tried merge branch
to default and it worked. Then we tried again original merge and it
went through.

We are on Windows, latest hg (2.3.1). Any idea? Hostile virus scanner?

Michal