In answer to a capo tuning question, one user suggested the use of a 'shim' (for lack of a better term, he actually suggested a .022" cut feeler gauge) between the fret board and strings under the capo near center between frets. I was thinking something similar as my capo clamps the strings to the fret board sharpening all 6 strings. Why isn't this answer 'liked' by the community at large? I'm going to try a few scraps of plastic or rubber of a thickness just less than the fret height to avoid the bend into sharpness and may get back with an answer (once given a nod by the Stack Exchange gods as a newbie).
The first thing I would get checked would be the action on the guitar. If it is high, the capo will stretch the strings out of tune. That can be adjusted. Another thing that can cause sharpening with a capo is large frets. Even with a well adjusted action, a capo and large frets can result in sharpening the note. Large frets have their own advantages so the guitars I own with large frets, I try not to capo, and I use them when I want to string bend.