[Plugin: Just One Category] Suddenly stopped working on new categories only

Just One Category has seemingly broken new categories only. I can add a new category, and assign a new message to it, but navigating to the category shows a Not Found error where the posting would normally go.

I can assign that same new message to a previously-existing category, and it shows up in that category page without any issues.

In the admin, if going to Posts > Categories, the new category shows as having a post assigned to it (i.e., a 1 in Posts column), but clicking on that link to the post takes me to the Posts page, where it shows no assigned posts.

Disabling Just One Category resolves these issues. (I do have the fix in place from the “No posts displayed in 3.3” thread, and JOC was working fine until just recently when I tried to add a new category and assign a post to it.)

Could this be related to the recent Jetpack changes?

http://wordpress.org/extend/plugins/just-one-category/