Typecheck error only when typechecking importing module

[PieterOlivier]

Describe the bug

When typechecking a specific (seemingly correct) Rascal module, no errors are generated.
But when typechecking a module that imports this module an error is generated:
"Invalid check return type; type of one or more subparts could not be inferred"

To Reproduce

1. Add two modules:

module sandbox::A

int() fGen() {
    int f() = 1;
    default int f() = 0;
    return f;
}

and:

module sandbox::C

import sandbox::A;

2. Make a whitespace change in module A and save it to trigger the typechecker. The module should typecheck ok.
3. Make a whitespace change in module B and save it to trigger the typechecker. A typecheck error will appear in module A.

Expected behavior
Typechecking should not result in errors (only a warning about the import of module A not being used).

Screenshots

Version info
VS Code extension version 0.12.2 and self-built VS Code extension with the latest rascal and rascal core from main.

Additional context

Note that changing module A like this:

module sandbox::A

int() fGen() {
    int f() = 1;
    default int f() = 0;
    
    int() returnF = f;
    return returnF;
}

makes the issue go away completely.

[PaulKlint]

Thanks for the excellent report! Unfortunately I cannot reproduce this with the latest version of the typechecker. I leave this open until that version is integrated in VSCode