Shares and Chirts

There are some people here in the Rio Grande Valley who have trouble with the SH and CH sounds when speaking. Words like chair, chalk, chain, or other words starting with ch become shair, shalk, and shain. Words that start with sh, like shower, show, and my name, Shaine will be butchered into chower, chow, and Chaine. I never could figure this out. I can't offer an explanation. It's just the way some people speak here in the valley.