Hi Leo,
Using the same sources as above:
_ Summary of Luftwaffe losses show two aircraft destroyed without enemy action on operational flight for I./JG 54 on 27 Dec 1944.
_ Flugzeugbestand und Bewegungsmeldungen for I./JG 54 on December 1944 show that while Fw 190 A of several subtypes were lost by enemy action, only Fw 190 A-8 (9 of them) were lost without enemy action. Same source show only two Fw 190 A-9 lost by I./JG 54 this month, both by enemy action. No trace in Rosipal list. Last data, during the month, I./JG 54 used 31 Fw 190 A-8 (14 at start of the month, received 17 and lost the same number destroyed or seriously damaged) compared to only 7 Fw 190 A-9 (7 at start, none received, two lost by enemy action and one sent to repair).
_ according to Rosipal, the collision occured "after an air battle", not during it. As Schrunden was then the base of I./JG 54, it is possible that the collision actually occured while they were returning to base after an air battle.
By the way Schrunden (then) = Skrunda, Latvia (now). See
http://en.wikipedia.org/wiki/Skrunda