So ... having spotted something not quite right and decided you can live with it, what do you instructors do when the student spots the same thing and draws it to your attention?
(An answer along the lines of "well done, I didn't think you'd notice that, but don't worry, you'll be OK with me in the aircraft" might not be unexpected ...)
On the other hand ... solo PPL hirer finds that the beacon isn't working, goes and finds duty instructor. Duty instructor says "are the strobes working? Well, in that case, seeing as how we don't have any other plane for you to take today, how's about you fail to notice the u/s beacon until you land, then report it on your return?" Seemed reasonable to me!