Howdy Sellener,
There are some installations of aircraft strobe light systems on aircraft wingtips that replace the need for a white tail navigation light.
Have attached a link to the Supplemental Type Certificate for the Whelen Company's strobe lighting system. Ask your flight school's mechanic(s) about the installation just to make sure the aircraft meets the requirements for lighting for night flight, but I'm pretty sure that's what's up in this case.
Supplemental Type Certificate