VBC emitting extra console output on warning with " error:"

Couldn't find an existing issue for this one (but could've missed it).

Compile the following piece of VB code in VS2015 with the "Implicit Type; Object Assumed" option set to "Warning":

Module Module1

    Sub Main()

        ' Causes build to fail
        Dim sEvent = String.Concat(" Error:", "Whatever")
        ' Won't cause build to fail
        Dim sEvent2 = String.Concat(" Another: ", "Whatever")
    End Sub

End Module

Both variable declarations will trigger a BC42020 warning. However, when the compiler encounters the sEvent declaration, it will include the line in the compiler output right after the warning, because it has the text " Error:" (leading space makes a difference).

This causes MSBuild/VS2015 to think the build failed and generate an strange error entry in the Errors window, even though only warnings were emitted during the build.