Looking at the map at http://www.civilwar.org/cedarcreekmap/2009%20Cedar%20Creek%20Appeal%20Map.pdf, Cox's Brigade of which the 2nd NC was part of came in contact with Keifer's 3rd Division which included the Artillery Division and the 7th Maine Battery.

From: http://www.history.army.mil/books/Staff-Rides/CedarCreek/ccsptdoc.htm
3d Division

1st Brigade

14th New Jersey

106th New York

151st New York

184th New York

87th Pennsylvania

10th Vermont

2d Brigade

6th Maryland

9th New York Heavy Artillery

110th Ohio

122d Ohio

126th Ohio

67th Pennsylvania

138th Pennsylvania

Artillery Brigade, Sixth Corps

5th Maine Artillery

1st NewYork Artillery Battery

Batteries C & G, 1st Rhode Island Artillery

Battery M, 5th US Artillery

Cox's Brigade

1st North Carolina

2d North Carolina

3d North Carolina

4th North Carolina

14th North Carolina

30th North Carolina

And from Cedar Creek Report, Commander, Rodes Division (OR, 43, 598-600) - http://www.history.army.mil/books/Staff-Rides/CedarCreek/RodD.htm
"In this advance Battle's brigade charged a battery in its front, capturing in addition to six guns many prisoners and a flag."

There is nothing in the 1st NY or 5th US Batteries report's that state they lost a flag. That's leaves the 5th Maine and 1st RI Batteries.

Again, not proof but still a possible answer.

Ed