I talked with my father today and he said that he has always wondered if the FW 190s were going to or returning from a mission -- he always assumed it was the latter.
He was most interested to learn about the Mistel operations. He said that he did not notice anything unusual about the planes (presumably they would have looked quite different with a drone on top).
I am attempting to insert a scan from his log book of his record of the incident:

https://plus.google.com/photos/11467...00600877604897

Not sure if it will work -- if not, any advice on inserting images would be most welcome.

Many thanks for the replies. Of all my father's war experiences, I think this is one that has haunted him the most. I very much appreciate the response to my query.
Sara