How to reproduce:
1. Open the attached project ("case-1105512-Unsafe Code.zip")
2. Notice the error regarding "unsafe code" in the console
3. Open the script ("UnsafeTest.cs") using Visual Studio
4. Notice that Visual Studio is giving warnings regarding the unsafe method
5. In the Editor, enable unsafe code (Edit -> Project Settings -> Player)
6. Notice that there aren't any errors in the console anymore
7. Go back to the Visual Studio and inspect the unsafe method

Expected results: Visual Studio no longer warns about the unsafe code
Actual results: Visual Studio continues to warn about the unsafe code

Reproducible with: 2018.3.9f1, 2019.1.0b7, 2019.2.0a8
Couldn't reproduce on 2017.4, because it doesn't allow to enable unsafe code via Project Settings

Notes:
1. Re-opening Visual Studio fixes the issue.