Other mistake: When the sniper fires her rifle at Joker after his rifle jams, she fires at him and strangely no shell casings are ejected. A few bursts later and her rifle does eject shell casings.
Other mistake: Private Pyle seems to be just as large in the bathroom scene with Hartman as he is in the Jelly Donut scene. In reality, it's just the same actor, but in the film's plot it implies he went through 12-22 weeks of boot camp under Hartman without ever losing any weight, even though Hartman was specifically trying to get him to.
Other mistake: In the first PT run if you look at their boots you see they have their trousers bloused, this doesn't happen in boot camp till week 3 or 4. In the next scene they are at drill and no bloused trousers.
Chosen answer: A Drill Instructor is always mad at the recruits in order to forge discipline. Private Pyle was the biggest screwup in the unit, thus creating more work for him.
Captain Defenestrator