I edit a page in rich text editor. I insert a new link using the link icon. I select a page from another space fom the History list. The link is created in the text. Saving the page the link points to the page of the selected title but in the space where the source page is.

Doing the same in wiki markup mode work as expected.

Inserting the link in the rich text editing as described above and instead of saving I switch to wiki markup mode clearly displays that the space prefix "spaceid:" is missing from the link.