Thank you, guys, but I assume this is a bug. The forum installed in a subfolder should not change any urls typed manually. I hope this information will help to detect a problem and fix it.
Here it is an example:
You may see, that the link points to the path out of the forum, let’s say ‘external url’ (for mind, my forum is located at https://www.cuba-platform.com/discuss).
The poster expects that anybody can follow the link later, as he(she) see on the screen - https://www.cuba-platform.com/store.
But actually forum redirects to another address https://www.cuba-platform.com/discuss/store which does not exist. This is because the forum has been installed in subfolder /discuss. I am sure that forum settings are correct 
. For that reason nobody knows how many cases with external links exist, and how many permanent rules should be predefined in the forum settings. The same problem is to have a plugin/php-script to handle such links.
As I remember, almost all external links posted by users were redirected to inexistent forum addresses, though those links were not located in forum. Users even cannot share a link to download page https://www.cuba-platform.com/download
I already have reported the same subfolder issues. Let me post it again, because here is a right place for them, I think. I filled some settings fields with custom values (terms of use, privacy policy etc) and tried to access them:
- Go to
https://www.cuba-platform.com/discuss/guidelines - Left click
https://www.cuba-platform.com/terms-of-use- redirects to wrong location. - Go back to guidelines.
- Left click
https://www.cuba-platform.com/privacy-policy- redirects to wrong location. - Return to guidelines.
- Left click
https://www.cuba-platform.com/faq- redirects to correct location. - Open browser console and click Back button (go back). It will show unstoppable redirect.
P.S. Currently I found that if I middle click the link (aka open the link in the new tab, Firefox) it opens the correct url! 