Changing double sharp to natural

I am using treble clef linked to TAB for 6-string guitar. I am in the key of E. I am trying to enter a D natural note as part of a chord.
1) When I enter the note on the TAB staff (B string, 3rd fret) it automatically puts it as a C dbl sharp (Cx); this is for quarter note entry
2) When I try putting the D natural on the treble clef, it messes up all the notes on the TAB side, moving them way up the fretboard
3) If I use half notes, for some reason it does it correctly - puts the D nat down on the B string, 3rd fret