Steps to reproduce:

1. Open attached project
2. Open script "Test" using MonoDevelop
3. Press F8 to build all assemblies
4. Notice error "The Name 'EditorWindow' does not denote a valid type ('not found')" There's also a warning that assembly for UnityScript failed to be loaded even though project doesn't use UnityScript anywhere

Reproduced with: 5.3.1f1, 5.3.6p3, 5.4.0p2, 5.5.0b1 (all use MD 5.9.6)
Not reproducible: 5.2.4f1 (MD 4.0.1)