My first issue so apologies if it's in the wrong format/place.
Environment data
dotnet --info output:
not installed (OSX, developing for Unity3D 5.6.0f3)
VS Code version: 1.12.2
C# Extension version: 1.9.0
Steps to reproduce
in any .cs file, add a using unnecessarily
Expected behavior
line with unnecessary using is underlined in green
Actual behavior
no underline - note that if the cursor is on the line, the suggestion light bulb correctly gives the option to 'Remove Unnecessary Usings'