Description:
"Blocking Mask" available in "Graphics Raycaster(Script)" component doesn't work when it set to "Nothing" with "Ignore Reserved Graphics" is checked.

Step to reproduce;
1. Download and Import "Unity Samples : UI " from Asset store
2. Select "Menu 3D" scene
3. Select "MainMenu" and "Settings" gameobjects.
4. Make sure that "Ignore Reserved Graphics" is checked under "Graphics Raycaster(Script)" component.
5. Change "Blocking Mask" value to "Nothing"
6. Play the scene.

Actual Result :
User can navigate the menu

Expected Result:
User shouldn't be able to navigate the menu.

Note:
It's not asset specific, user can face this even if he creates his own UI.

Reproducible on:
Unity 2018.1.0b1 , 2018.1.0a7 , 2018.1.0a3 , 2018.1.0a1 , 2017.3.0f3 , 2017.2.0f3 , 2017.1.1f1 , 5.6.5f1

Environment:
Occurring on both Windows and Mac