OmniSharp doesn't recognize mscorlib namespaces for a buildable project

Environment data

dotnet --info output:

.NET Command Line Tools (2.1.3)

Product Information:
 Version:            2.1.3
 Commit SHA-1 hash:  a0ca411ca5

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.13
 OS Platform: Darwin
 RID:         osx.10.12-x64
 Base Path:   /usr/local/share/dotnet/sdk/2.1.3/

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.4
  Build    : 7f262f453d8c8479b9af91d34c013b3aa05bc1ff

• VSCode Version: Code 1.19.3 (7c4205b5c6e52a53b81c69d2b2dc8a627abaa0ba, 2018-01-25T10:25:01.248Z)
• OS Version: Darwin x64 17.4.0
• Extensions:

Extension	Author (truncated)	Version
csharp	ms-	1.13.1

Steps to reproduce

Have a project. Build it successfully with dotnet build. Open it in VSCode.

Expected behavior

OmniSharp does its job.

Actual behavior

Lots of errors like this: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)

[barcexwiki]

I have the same problem. I had to roll back from 1.14.0 to 1.13.1 to get it fixed.

[cartermp]

This doesn’t reproduce (TargetFrameworks with a single TFM) anymore on the latest version of the plugin for me. So I’ll close this out.