The uniform of cavalry captain Staniewski on the dance ball resembles the uniform of a polish officer, noticed by the bright front, while the actual uniform shared the same color. In later versions the pants had different color than the coat.
The guns in the arsenal are bolt action carbines. The very first bolt action firearms were not adopted by any army before the 1840s, i.e. a decade after the historical events the film is based on. Except for the first salvo fired, they also clearly use smokeless gunpowder introduced even later. One would expect caplock carbines using black powder in this setting. It seems likely that they used the equipment of the Polish cavalry unit serving as extras.
Princess Katerina has "Tschernikoff" as her last name. In Russian the ending "off" is used for men only. The female ending in this case is "offa" so she should have been called "Tschernikoffa".