One of our users was running hgsubversion and the keyword extension enabled at the same time. When he pulled from subversion his resulting changeset was corrupted. Part of the source code was missing. We re-ran the pull on a repo without keyword enabled and it was correctly formed.
I know that there may not be much hgsubversion can do about this due to the way extensions stack. But perhaps we could print a warning if keyword is enabled during a pull?