When the Shrovetide (Maslenitsa) scene was being filmed the temperature on the lake grew up to +12 centigrade and the ice could have broken with all the actors and decorations. So the movie makers had to cover it with dry ice and use liquid nitrogen constantly.
In scenes that take place in 1885, the cadets are carrying Mosin-Nagant rifles. This rifle did not exist at the time. It was introduced into service in 1891. The standard Russian infantry arm in the 1880's was the Berdan rifle.