Type checker doesn't warn about "shadowing" nonterminal type

[tvdstorm]

The type checker does not provide diagnostics about name collisions between ordinary types (or at least aliases) and nonterminal types. I've been able to narrow it down to the snippets below. I have experienced that a call like the first foo in main did not get called, so I expect that the arbitrary ordering of imports could is a cause of that (but I can't reproduce the behavior).

module Bug1

syntax Foo = "foo";

module Bug2

import Bug1;
import IO;

alias Foo = str; // no error or warning

void foo(Foo foo) {
    println("boom");
}

void main() {
    foo("foo"); // no error, boom gets printed.
    foo((Foo)`foo`); // error: `str or Foo` possibly not supported by parser generator
}