Language Service does not show FS0247 error

[cartermp]

Using 16.0, but also reproduces in 15.9

1. Create a new project
2. Replace the contents of the first file with this:

namespace A

    module B = begin end

3. Create a new file and replace its contents with this:

namespace A.B

    type DU =
        | X of float
        | Y of float

Expected:

• Error in the error list and in the editor
• FS0247 - A namespace and module named 'A.b' both occur in two parts of this assembly

Actual:

• Nothing in the editor and nothing in the error list