"unassigned" search keyword

I'm having trouble using the 'unassigned' keyword to search for issues. Starting with the most basic search: '#unassigned'. Running this, I only get back the unassigned issues within a particular project (which happens to be TEST). Context is set to 'Everything'.

Probably related, I note when typing this out that I don't get an autocomplete offering that is just the unassigned keyword, but rather all the options are '#{Unassigned in xx}', where xx is a project code. Notably, however, selecting any of those options also yields nothing, except for '#{Unassigned in TEST}', which returns the same set of results as #unassigned by itself does. All of this is holds even when I try changing the context away from 'Everything'.

The docs gives an example of finding all the unassigned tasks within a project. Following this example, things get even stranger. For example, 'project:xx #unassigned' yields no results and underlines in red the unassigned keyword as though it is invalid syntax. However, after changing the project code to TEST, the red underline immediately goes away and the search works great. It's like I can't search in any other project.

Is there something obvious here that I'm missing?