Nested fetch-groups specified with annotation metadata don't work properly.
E.g. with metadata like:

@FetchGroups({
      @FetchGroup(name="simple",
members={
@Persistent(name="_b")
}),
@FetchGroup(name="nested",
fetchGroups={"simple"},
members={})
})

Using DetachAllOnCommit=true and fetching with the "nested" group yields:

javax.jdo.JDODetachedFieldAccessException: You have just attempted to access field "_b" yet this field was not detached when you detached the object. Either dont access this field, or detach it when detaching the object.

The equivalent metadata declared via xml works fine.