Yeah, the main reason this function is being used is so that the map-based posts don't lead to the blog-based posts. This is the best approach to keep those items separate.

Shockingly, after looking, this is correct wordpress behaviour....

http://codex.wordpress.org/Function_Reference/next_post_link

in_same_cat
(boolean) Indicates whether next post must be within the same category as the current post. If set to TRUE, only posts from the current category will be displayed. Options are:

* TRUE
* FALSE (Default)

Note that if the post is in both the parent and subcategory, or more than one category, the next post link will lead to the next post in any of those categories.

Not a fan of this behaviour, it makes no sense to me to include the parents, especially for this theme. May have to hack the code on this one....

A standard WordPress function is being used for these links, so I'm not 100% sure, but it seems to be grabbing the parent category (I.e. "locations") and not the child categories (I.e. "Mercer Island").

Yes that is how it should behave I believe...but it is not.

See your example site: http://www.lakewaparks.com

1. In the Menu select Mercer Island.
2. On the bottom scroller, we see three parks in the category (Groveland, Clark, and Luther).
3. View details of Groveland.
4. Using the bottom left arrows scroll to the next: which will be Clarke, then the next: Luther.
5. Then the next: Madison Park (and breadcrumbs lose Mercer Island, since not in Mercer Island Category).
6. Then the next: Madrona... and so on

Seems to be a bug, unless I am misunderstanding how it should work, I would think on Luther it would either stop paginating forward or lap to the first entry in Mercer Island category.

Oh and if you select the back from Groveland, it does not work as well (goes to a park in Kirkland).

Hope that makes sense.... :)

The "next/previous" links on the single.php page link to posts in the same category as the current post. Does that help answer/address your question?

It seems that when, for example, you select a category to view, when you navigate through the posts from the single.php context, you lose the query and it starts navigating through all the posts. You can see this by viewing the breadcrumbs as well.