Steps to reproduce:

• Go to a page in a namespace that allows subpages (e.g. "Talk:Bar").
• Save or preview an edit with [[:/Foo]] in the summary.
• Check the rendered summary.

Actual results:

• The link points to the subpage ("Talk:Bar/Foo").

Expected results:

• The link points to the page in the main namespace ("/Foo"), as [[:/Foo]] does in the wikitext.

See this edit and its summary source for an actual example.