The problem is that you are using a numeric only ID. Seems that such IDs are claimed as build number IDs somewhere in Jenkins core (Build or Run instance). So my URL actually will never be resolved.
If you use an id with character in it m1000 then everything works as expected. That means I can do nothing in my plugin here. You can try to file that as bug in core but I doubt that this will be fixed by someone as an actual build number can also resolve to the ID you have chosen.
The problem is that you are using a numeric only ID. Seems that such IDs are claimed as build number IDs somewhere in Jenkins core (Build or Run instance). So my URL actually will never be resolved.
If you use an id with character in it like {{m1000}} then everything works as expected. That means I can do nothing in my plugin here. You can try to file that as bug in core but I doubt that this will be fixed by someone as an actual build number can also resolve to the ID you have chosen.