Relative urls like "/pics/image.png" marked as external link

Hello,
we run phpBB for testing on a local server with a different domain.tld as the "production-server".

To be able to see if all is working fine we replace the "http://domain.tld/pics/image.png" in the phpbb_posts table to "/pics/image.png". Then this links are marked as external link.

Maybe this can be fixed?

Thank You
