mtree: exclude keywords from being checked

In mtree, how do I exclude keywords present in the specification from being 
checked against the on-filesystem value? E.g, the spec contains md5, but I 
don't want mtree to compare that to the actual files?

The manpage suggests -k/-R would be what I want, but that seems to only make 
a difference when generating (-c) a specification, not when comparing to one.