Steps to Reproduce:

• Copy a page's URL into clipboard, e.g. https://www.wikidata.org/wiki/Wikidata:Events/Wikidata_Wochenende_Ulm_2020/Programm
• Go to Wikisite, e.g. https://www.wikidata.org/wiki/Wikidata:Events/Wikidata_Wochenende_Ulm_2020
• Click "Edit" on top -> opens the Visual Editor
• Mark a section of text; click on "Hyperlink generator button" of the Visual editor
• Paste the clipboard's URL into the appearing field ("Wikidata" selected as scope)
• The correct page is matched and auto-suggested ; click on it
• link appears correct in the live preview (is blue)
• click on publish changes
• publish changes

Actual Results:

• link is broken (red), and links to "Events/Wikidata_Wochenende_Ulm_2020/Programm"

Expected Results:

• link is correct (blue, and links to "Wikidata:Events/Wikidata_Wochenende_Ulm_2020/Programm"

User Info: Firefox 70.0 (64-bit) on macOS Catalina 10.15.5