fixes #4194, #4459 - add main_app to root_path references for isolated engines
(cherry picked from commit 33b384f2b29363014608ac1b85061b5a8b4791d5)
fixes #4194, #4459 - add main_app to root_path references for isolated engines
(cherry picked from commit 33b384f2b29363014608ac1b85061b5a8b4791d5)