Steps to reproduce:
1. Open attached project or create a new one.
2. Right click in the "Project" window.
3. Select "Create->C# Script".
4. Leave the default script name (do not select anything else and do not click somewhere else in the Editor).
5. While the name of the script is still highlighted in blue, right click on the script and select "Delete" option.
6. Notice that the "Console" window outputs this error message:
"Weaver failure: unable to locate assemblies (no matching project) for: Temp/Assembly-CSharp.dll
UnityEditor.Scripting.Serialization.Weaver:WeaveUnetFromEditor(String, String, String, String, Boolean)"
7. Press "Clear" button in the "Console" window and notice that the error message disappears.
8. Try entering the play mode.

Actual result:
The Editor informs that "All compiler errors have to be fixed before you can enter playmode!". However, the script that caused the issue was deleted and the error message is no longer visible in the "Console" window.

Expected result:
The user should be able to enter the play mode when there are no compiler errors visible in the "Console" window.

Workaround:
Re-import all the assets or restart the Editor.

Reproduced with:
5.1.0f3, 5.2.4f1, 5.3.4f1, 5.3.5p1, 5.3.5f1, 5.4.0b18.