Buran was carried by the Bison bomber too, and an accident occured once! The tarmac got damaged by permafrost at the Kapustin Yar airfield and the plane slipped away. The undercarriage broke but the Shuttle was saved (january 1983).
Another time, one of the Bison's engines was emitting smoke, while up in the air whille a Shuttle was on top (I saw a brief video sequence last week about it).
If only the Soviets and the Russians had a much better press coverage of the manned space program. It's amazing what they went through: near misses, exploding engines, sickness in space, almost drowned cosmonauts...And from 1971, they all always came back alive.

Raoul