Your tip on checking on another guitar worked for me, because on my acoustic guitar, with more space between the strings, I had same issue. So after that,  and checking a basic tutorial of Caren Armstrong (The Basic Chords: Position and Placement), I found out my nails on my left hand were a little little little bit too long :-), I couldn't see/feel it at first. And now I can play these open chords as well without demping other strings.