Mercurial subrepros not getting updated

Hi guys,

I'm seeing a problem whereby TeamCity will not update subrepositories to the revision that the parent repository is tied to? Consider this:

Repro A references Subrepro B
A change is committed to Subrepro B
The change to .hgsubstate is commited to Repro A, so you know which version of Subrepro B to use

Running TeamCity, it updates ReproA, but does not correct the version of Subrepro B unless I delete the local cache and start again? Note I'm not trying to get it to pick up the *latest* changes - just update to the correct revision that ReproA requires? (which for me everywhere else happens automatically when I try to update Repro A).

What do I need to do to get this behaviour?

Many thanks,

James