Steps to reproduce the issue

Default Editor is "Editor - TinyMCE".
In a article or Custom Module add Text with a link "/" or "/example"
Switch off editor without saving. Href attribut has wrong content.
Change href attribut to "/", switch on and off editor an href attribut is wrong again

The HREF attribute is not changed by Joomla when saving.

Same with JCE works as expected.

Expected result

Link tags: <a href="/">Text</a> or <a href="/example">Text</a>

Actual result

Link tag: <a href="http://your.domain">Text</a> <a href="example">Text</a>

System information (as much as possible)

Joomla 3.10
Firefox macos

Additional comments