The vc-cancel-version (bound to C-x v c) for the ClearCase backend will remove an extra version. This will happen if both conditions below are met:
* The variable clearcase-rmbranch-on-revert-flag is set to t
* The version to be canceled is the second version on the branch (e.g /main/some_branch/2)
In this case, vc-clearcase-cancel-version will delete the selected version (/main/some_branch/2 in our example), than it will also delete the branch (/main/some_branch in our example) and the /main/some_branch/1 revision will be lost too.
This happens because `clearcase-maybe-set-vc-state' is called before the check to remove the branch.