3
Nothing new, here. This has been that way for a long time.
The url xoopscode tag expects a fully qualified URL. Partials lead to security exposures very quickly. There is no one size fits all way to resolve scheme-less URLs. XOOPS can for example work fine in a directory under a domain.
There is a siteurl tag which always prepends the full XOOPS_URL with a trailing slash. That is useful when transferring content between a prototype and a production system without changes.