Every now and then while playing I notice when releasing my finger off of a string after fretting it the open string note or its harmonic will be played, quiet but enough to be heard amongst the notes being played by me. Is this problem down to a poor setup on my guitar or sloppy technique, and how could I go about correcting this?
well, you could start by posting on one forum at a time.

depends on where the harmonics are occurring. if they're at the standard spots (i.e. 5th, 7th, 12th frets, etc.) then it's just a question of rectifying your technique and learning to mute better.

if they're not at the standard spots, check your intonation.

i'd bet you that it's probably your technique - if your intonation was THAT off you'd probably have noticed by now.
Anfangen ist leicht, Beharren eine Kunst.
It's your technique. Work on muting.
Quote by Geldin
Junior's usually at least a little terse, but he knows his stuff. I've always read his posts in a grouchy grandfather voice, a grouchy grandfather with a huge stiffy for alternate picking.
Besides that, he's right this time. As usual.