Condition 'path' results in 'Page Not Found', but reaction blocks are populated?

I've created a very simple context, the condition is Path == test and the reaction is to put some content into blocks on the page.
The blocks on the rendered page are populated correctly, but the page title and $content read "Page Not Found", and there is an error log entry reading "page not found" for the context's url (e.g. www.site.com/test).

What might be my next steps re. diagnosing this? Any particular file/function that I should breakpoint? (there are a whole bunch of them)