It's a warning directed solely at compiler authors (hence -DDEBUG). If a lot of glomming is happening, it might be due to some scoping or dependency analysis bug -- e.g. perhaps OccAnal isn't putting bindings in proper dependency order, or perhaps some plugin is gratuitously scrambling the order of the top level definitions. Or it might be legitimate, as in your case.
Perhaps adding a Note with the code that generates the warning (or wherever you looked -- where was that?) would be better. I always like to look for ways to reply not just to Gergo but to all the future Gergos who stumble over this.
Gergo might you offer a patch?
Simon