Backlinks update changes an absolute reference to the moved page into one relative to the current wiki

Upon copy of a page with a relative link vs a page with absolute link, the link will not point to the same place, we should respect that.

hmmm right, actually I'm not 100% sure it would be a problem right now (but maybe you tested it), but as I'm working on XWIKI-12987 to actually keep the relative links as part of a copy / move we might indeed hit bugs in the future with that behaviour, e.g. if you copy that page to another space containing a page C.