There was one particularly notable incident between the USAAF and VVS in November 1944: P-38 squadrons under Colonel Clarence T. Edwinson were supporting a Soviet advance in eastern Yugoslavia and strafed a motor column. An error in navigation meant they were fifty miles off their intended target and the column was Russian; casualties included the Corps Commander Lieutenant General G. P. Kotov. Soviet Yak-3 fighters from Nis took off and engaged the P-38s, details vary in different accounts but it seems 2-4 aircraft on each side were shot down before the two sides disengaged. (Details from Barrett Tillman's Forgotten Fifteenth.)

More widespread or deliberate engagements between the air forces seem unlikely, though there are other unconfirmed stories such as top-scoring Allied ace Ivan Kozhedub being bounced by P-51s (presumably mistaking his La-7 for an Fw 190) and having to shoot down two of his attackers. There were scores of friendly fire incidents during the war, air-to-air, ground-to-air and air-to-ground (an American Lieutenant General, Lesley McNair, was killed by 8th Air Force bombing in Normandy), it's certainly possible that there were other incidents, but the /r/history post suggesting multiple aces over Soviet aircraft is highly implausible.