Wrong behavior when clicking a Gancio AP handle in Mastodon

Clicking on a mentioned Gancio AP user/handle (@relay@instance.tld) in Mastodon leads to the wrong behavior. Normally a mentioned ActivityPub user/handle (mentioning works like it should) gives a link without a visible instance name. When you click on it the user profile is opened in the Mastodon interface. This works correctly for all (AFAIK) fediverse projects. But because a Gancio handle only has the instance root URL as the handle URL (or Actor ID?) there goes something wrong, it opens the external instance URL. Therefore also hovering in the new version 4.3 won't work.

This is happening:

<span class="h-card" translate="no"><a href="https://gancio-instance.tld" class="u-url mention status-link unhandled-link" title="https://gancio-instance.tld/">@<span>relay</span></a></span>

But it should be like this:

<span class="h-card" translate="no"><a href="/@relay@gancio-instance.tld" class="u-url mention status-link" title="@relay@gancio-instance.tld">@<span>relay</span></a></span>

I don't think this is a Mastodon bug, because other fediverse software seems to work. I'm not a developer, but I guess this can be solved with somehow make sure the user @relay has it's own URL, like https://gancio-instance.tld/user/relay or https://gancio-instance.tld/@relay.