Wrong display of diff line numbers in case of additions

Apparently we output wrong line numbers in diff when there was additions: the line numbers are erratic, sometimes we find twice the same line number, or we find back a previous number when we are supposed to keep incrementing.

Those problems apparently appears only with additions, numbers look good with change deletion.

See screenshot for an example extracted from https://www.xwiki.org/xwiki/bin/view/Roadmaps/?viewer=changes&rev1=714.1&rev2=716.1&