Vicki,
I was looking thru CMSR's on footnote.com and found Isaac Riddle 11 Regt. Tex Inf detached to QM Dept. at Mt. Pleasant,Texas by SO 156 dated Jun 22, 1864. I had seen a note in Traylor Russell's "History of Titus County Texas" that Isaac was at Mt Pleasant in wagon shop. It appears Isaac Riddle got sick and came back to Titus Co on furlough and never when back to the 11th.
Mike