It may be an isolated instance (although probably not), but the QM records of the Kentucky "Orphan" Brigade (in the AOT from 1862 - late 1864) indicate very large issues of "caps" and "infantry caps" throughout the time range of the existing records - mid-1862 through February 1865. In fact, among the final issues recorded in early 1865 were caps. Throughout most of the war, caps were issued in sufficient numbers to sometimes cover entire regiments. I'm assuming these were kepis ... they apparently weren't traditional hats.

Doubtless these caps were of different styles, from different manufacturers, but maybe we can judge somewhat from a surviving example. One kepi-style cap identified to a Kentucky soldier survives - said to have been worn at Chickamauga by the color-bearer of the 2nd Kentucky Infantry (see http://www.rootsweb.com/~orphanhm/uniform3.htm ). It's made of gray wool on a cotton warp, but not a jean material. It does have a glazed bill and chin strap.

In spite of the period records, KY soldier writings make it clear that the "slouch hat" was more popular. One can only speculate on what the soldiers did with all the issued caps. Or did they actually wear them???