Error messages: "FS0039 : The value or constructor 'SomeNamespace' is not defined"

(Edit 2nd March 2019: This issue is not well explained here. Please jump to my post further down with a screenshot with white background for a better and quite brief explanation.)

When typing the name of a namespace and trying to dot into it, these errors will appear in the Error List pane.

E.g. type "System".

Edit, clarification: You need to type `System` or `System.` as when to use qualified access in a function or something, and not after the `open` keyword.

FS0039 : The value or constructor 'System' is not defined.
FS0599 : Missing qualification after '.'

CASE 1: The namespace is actually accessible, so the first error reported is not correct. Intellisense will still work, and allow namespaces and members to be selected from the list that pops up when dotting.

The second error is sufficient in this case.

CASE 2: If you don't dot into it, the second error message is not there. The first error message is still there and still wrong, and needs to be replaced with a correct error message in this case.

If not a namespace, but something else valid, the error message isn't there, which is ok.

#### Related information

* Windows 10
* Visual Studio 2017, v 15.2 (26430.6) Release
* Visual F# Tools, v 15.4.1.17051701 (nightly builds)
* Severity: Trivial. Lowest priority. Only a nuisance.

I haven't added this to the list of error reporting improvements, because this is a bug, and not just an improvement request. Am I wrong in doing so? Perhaps it is practical to add it?