Let me give you an example of why this is a problem
If you go
to my photopost site, you will see some categories under "Collections". There is "Arrowhead", "Knives" and "Calculator". But if you click on any of those, you get a photo of a Phantom F4 Jet Fighter. That is very confusing to those that want to view photos. If they click "Arrowhead" they expect the next view to be related to Arrowheads.
Now, that is why I would rather specify a fixed photo for all galleries. I could put a generic photo.
It would be better though, that if one clicks a collection of photos under a category, that the gallery for those photos, would be related to the category.
Just my thoughts on this. I think all navigations should be a user friendly interfaces.