Why does hg choke when I veto resource forks on Samba?

I have a few users using Mercurial over Linux Samba shares, mounted on their Macs.

The Samba server has the following veto rules (well discussed both here on this site and elsewhere) to prevent Macs from creating resource forks, which wreak havoc with all sorts of things, especially on developers' directories:

veto files = /._*/.DS_Store/
delete veto files = yes

The problem is that sometimes, randomly, Mercurial will choke with this error:

$ hg ci
trouble committing stylesheets/custom.css!
transaction abort!
rollback completed
abort: Permission denied: '/Volumes/xxx/yyy/.hg/store/data/stylesheets/._custom.css.i-JdxA5R'

Why is Mercurial trying to create a resource fork inside its own data store?

If I comment the veto rule, the commit succeeds, but it leaves no such resource fork on the server. So it appears to be a temporary resource fork, or that of a temporary file.

How can I prevent hg from creating it, or ignore the error, or make Samba swallow it silently?

Edit: I suppose (but I'm not certain) hg is creating a temp file called custom.css.i-JdxA5R and for some reason OS X tries to attach a resource fork to it. When that fails, as it's vetoed by Samba, OS X returns an error for the entire temp file operation.