PIE captures mouse when "Game Gets Mouse Control" is disabled

When entering PIE, the mouse is captured by the viewport regardless of the "Game Gets Mouse Control" setting.

Regression:
No - Same behavior occurs in 4.17.2

1. Open UE4 Editor
2. Navigate to Edit->Editor Preferences->Level Editor->Play
3. Ensure that Play in Editor->Game Gets Mouse Control is disabled
4. PIE

Result:
The mouse is instantly captured when PIE starts

Expected:
With the option disabled, the viewport must be clicked to capture the mouse.