Steps to reproduce the issue

Create a Joomla site (2.x or 3.x) with featured articles as the homepage
Browse to site.com/17-pages (as an example - this is where I first saw it). This should not exist.

Expected result

404 error

Actual result

Instead of giving a 404, this resolves the homepage. I've tested this with 2.x and 3.x with different URLs which don't exist, same problem.

System information (as much as possible)

Tested on both 2.x environment and 3.x environment with 17-pages, 18-pages etc - all seem to be loading the homepage. Also asked others to test.

Additional comments

This has potentially very serious SEO implications!