Having a brush drag it along will give unpredicatble results, cause lag (as the server will need to calculate a LOT of networked physics) and the prop may even 'freak out' and escape from confinement.
If the constraint stopped working than I suggest there is something else at fault, maybe you forgot to select part of the setup, made a typo or accidentally changed something else. There's no logical reason that something would work in one map and not in another unless they aren't the same. Try doing it over again double checking everything, in the main map.