Private functions can be called in other blueprints

Private functions within a blueprint can be called from other blueprints. A warning does appear but the function is run despite this warning.

1. Download, unzip, open attached project
2. Open map "test"
3. Press PIE

Results:

"Private function called" appears on screen.

Expected:

Either error message appears warning that private function cannot be run and no text appears on screen or no text appears on screen with no warning.