Mercurial repository corruption

This is somewhat related to this question but is a different question.

We have a central Hg repository, served to users via SSH and mercurial-server. We have a number of Mac, Linux and Windows clients connecting to it.

It has happened twice now that one of the Windows users has corrupted their repository, then pushed back to the central one corrupting it. I want to write an incoming hook script on the central repository to prevent a transaction from being accepted if it will corrupt the central repo.

Although unfortunately I don't know enough about Mercurial to write such a script. Any possibility that someone else has come across this? Personally I'm not quite sure why hg doesn't do this by default.