Multiple heads with default "hg push"

The xemacs/XEmacs repository is experiencing multiple heads. This is contrary to the documentation of hg push, which says it will not create multiple heads unless -force is used. In at least one occurance I know that -force was not used. This bug has already effectively reverted a beta release (.hgtags is head-specific, so the release tag that would have allowed convenient access is not visible from tip). The net result is denial of service, which is a serious problem.