Number of posts per page - URL problem

By default this forum displays 15 posts per thread.

Users have option to change this value at Edit Options panel.

An example url from a multi-page thread:
vBSEO Functions for Extensibility

I posted the URL above when i had the posts per thread option set to default. (15)

I changed this option to "Show 20 posts per page" and the same URL redirects me to different content.
This also applies to permalinks.

vBSEO Functions for Extensibility (going to post #61)

vBSEO Functions for Extensibility (not going to any posts after the change but starting from #81)

So, if a member uses a custom "post per page" option instead of the forum default or you change this setting at the AdminCP, the URL's will lose their functionality. How to prevent this?

Another problem is the deleted posts. If previous posts deleted from the thread, -posted permalinks or threads' page links- will lose their functionality, too.

Yes, it's a known issue and occurs with default vBulletin as well: Permalink reliant on user settings