I have an issue where a url ending /post or even /post/123 and in my case /post/category just produces a partial page of html as text.
Permalink custom structure is: /post/%post_id%/%postname%
Visiting the link produces the following:
title='1 topic' rel="tag" style='font-size: 8pt;'>spiders
<div id="footer" role="contentinfo">
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