Thanks for the replies. Perhaps I should have been more specific. In the first two photos (taken, perhaps, seconds apart--where did the Mantel go?), von H is wearing a Garde helmet with vaulted scales, but the front peak is rounded (not angled, as it should be), the spike cone is not fluted (as it should be), and the spike base is not cruciform (as it should be). It's a Garde officer helmet, yes, but not a General's, or General à la suite helmet.
The third photo is even more inexplicable, as the helmet is a run of the mill Preußen line officer helmet, albeit with vaulted scales.
I find this totally bizarre.