No it does not happen in jail all the time, it does happen in long term prison containments. With violent and clearly mentally unstable individuals. I have been to jail, and prison, not ashamed. Sorry to say it doesn't happen as often as they claim it to. Even when it does it is between consenting homosexuals. I am going to try and find the documentary on it.
Accoriding to the documentary it happens more often in youth detainment centers, and maximum security centers, and that was due to the gang initiative and the lack of outside connect. Which I would also say all these individuals were already outside the norm of society.
You'll forgive me, I trust, if I do not believe you, considering my own personal experiences and they plethora of clinical research and simple statistics available.
BTW, a "documentary" does not proof make, sorry. A documentary is, for all intents and purposes, the opinions of the producer.
In any area where people are removed from the opposite sex for prolonged periods, jail, ship board (especially back in the day), etc. a number of people will turn towards their own gender to satisfy the single most basic instinct in the human animal, sex. When those who are hetero are returned to the general society, they also return to their normal sexual activities, ie sex with the opposite gender.
Like most who remain willfully ignorant on the matter, you confuse, and refuse to seperate, same-gendered sex with homosexuality.