hmm. if we think about it, during the final assembly stage of the guitar where they are hung up waiting for the finish to dry (few days to weeks), they are not strung up yet.
So following the "argument" that changing tension in the neck will cause it to warp, shouldn't the neck of originally unstrung guitars warp if we add strings to them? But we all know that this is ridiculous.
Penko: that be a question of technique already. It's sloppy playing where I believe you do unintentional pull-offs when you remove your fingers off the strings. Try to work on the pressure/touch of your playing.