Found that on "Google Advanced Search Books."
"History of the Flag of the United States of America: And of the Naval and..."
By George Henry Preble. (1882)
Page 582.
This battle (when Sheridan came back) was 3rd Winchester. Sounds like the "Staff Flag" was captured when the Confederates launched their "surprise" attack.
Also has captured Confederate flags as well.
Now there seems to be a controversy that NO US Regulars regiments lost a flag or flags during the war. I know that is untrue for the simple fact at Gettysburg the 11th US Regulars in their OR report admitted to losing their Regimental Flag.
At the battle of Murfreesboro, General Bragg had a list of captured Union Flags.
From the Book "That Body of Brave Men." By Mark W. Johnson Page 694
Bragg had on his list in "Entry Six: "Silk Stars and Stripes" captured by the 5th Arkansas of Cleburne's division. Private J.K. Leslie, Company C (5th Ark) captured this flag. Now in the book Mr. Johnson states that the 5th Arkansas did not fight anywhere near the Regulars in the battle. Also only the two battalions of the 18th Regulars had National Flags. Neither of them were captured.
Bragg's "Entry Seven: "Captured by Sgt. John F. Levin, 3rd Confederate." The flag he captured just might be a Regulars regimental flag. The flag was "Dark Blue Silk, indicating it might have belonged to a Regulars regiment, the scroll on the flag had no regimental number." The flag arrived at the museum at West Point, which it might still be there currently.
I don't have Bragg's list of captured Union flags at the battle of Murfreesboro, but I bet it would be interesting.
Have a good Sunday!
Shawn