Proposal:
When both foo.ml and bar.ml define zot and quux.ml opens both Foo and 
Bar, there should be a warning (when compiling quux) about Foo.zot being 
shadowed by Bar.zot (or vice versa, depending on the order of the open 
statements).
If you think this is an overkill, please at least consider issuing the 
warning when zot is used in quux.ml.
If you think that is also an overkill, please at least consider issuing 
the warning when foo=quux.