goldensandmusic

I have a mic epiphone casino probably 2013 made. Good sound good play, I choosed it from 10 same guitars. There is an intersting issue with tuning. When you play for while a normal guitar go flat, but this guitar go sharp allways. Whole strings go sharp after a time. Dont know whats happening if guitar expands or strech itself, any ideas? There is no out of tune problem so far, but whole string go sharp together, not too much but it has to be flat or loosen :)