Oh come on. When will people realize that these movies are made for ENTERTAINMENT! They are films, not documentaries, if you want to see the exact story of the Tsar on screen watch The Last of the Tsars or something. They never, ever try to make it perfectly the same, it's the same when they're translating books into movies, things have to bee changed. To be historically accurate is not the point of the film.
The scene between Tatiana and the guard is distasteful to us, but not to the general public who don't know that much about NAOTMAA because they haven't specially researched it. To people who don't know that much about the Romanovs, that scene just shows a scared and confused girl, who's 21 and is being repressed in every-way, socially and sexually. And to be honest, there's no real proof one of OTMA would not have done something like that. Like dimitri said, no one knows how they would have reacted to being put in captivity and having their whole life turned upside down so suddenly, especially at those ages, 23, 21, 19, 17. People those ages have usually developed sexually, and these days most are sexually active by then. It's no stretch to imagine that Tatiana, or any one of the girls secretly wanted to try sex and were feeling sexually repressed. OTMA were not saints, they were normal people like you and me, who would have had normal feelings like you and me.
I'm not saying it's likely that this actually happened, it's probably very unlikely. It's just not impossible.