Update about the link overlap problem : solved!
Grrr, I thought about it while falling asleep : maybe poEdit is keeping the older version in the file. So instead of finding the string by typing "trackback" in poEdit, I did in NotePad, and found out that there are two instances of the "Trackback an URI (separate...)" string : one in simple edit mode, one in advanced.
As my settings where on "When starting a post, show: advanced", I set it back to simple, and there you go : it works. The problem resides in the advanced part.
And that's where I understood : while the simple edit mode uses one string, the advanced mode uses two, "Trackback an URI" and "(separate...)". Of course I couldn't find the second string, as I was looking for a link in a string containing both Trackback and an Href...
Well, in the end, you were right Allusion : there was a missing closing tag at the end of the second "(separate...)" string.
Now I'm gonna find a hat and eat it. And update to the latest nightly.
Thanks for listening.