NaturalId not working when used with Version?

I have a class that has both a version (sql timestamp) and a natural id value. When testing this with hbm mappings, these work fine when placed in the file such that the natural-id tag is prior to the version tag. However, when FNH generates the mapping document, I can see that the version tag is before the natural-id tag. This results in an error when compiling the mappings that states that natural-id is an invalid child element. This works with either version or natural-id in isolation, but fails when these are combined in the same classmap.