Pipe or closing brackets in a wiki link reference or wiki image alternative text break the link or image in CommonMark Markdown 1.2

When rendering the following xwiki/2.1 content to markdown/1.2 and parsing the result back:

[[image:a.png||alt="x~|y"]]

Expected: an image of a.png with the alternative text "x|y".
Actual: it's rendered as

![[x|y|a.png]]

and read back with the alternative text "x" and the reference "y|a.png". Similarly, a wiki link reference containing a pipe or "]]" is truncated or keeps backslashes when read back.