some Jews survived by performing acts of service and skill to their Nazi masters - a moral choice I cannot judge, that was in some cases misconstrued by soviet commanders as criminal.'

Kapos were instrumental to the operation of concentration camps. They were often informers and enforcers for the guards. Many of them were beaten to death by their fellow inmates when the nazis evacuated during the advancement of Allied forces. That was if they made it to the end of the war. Kapos were regularly murdered in their sleep or shanked by other inmates if the kapo was seen as an asshole.

This wasn't the case with all kapos, as a lot were involved in resistance efforts. Some would even take jobs for the SS doing whatever so they could get extra rations, which they smuggled back to their barracks at great risk to themselves (IIRC Elie Wiesel had this kind of kapo and its partly the reason he survived).

Anywho, my point is it's not surprising soviets liberating the camps acted the way they did towards kapos because a lot of them had been collaborators. If there was no one alive to vouch for them, it makes sense the soviets would imprison them. They probably thought what they were doing was humane.