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.

Private functions are listed in external blueprints