Thank you, kwalker and Geoff, for taking a look and for your feedback.
Geoff: I usually get that kind of star profiles when imaging with the 2x barlow lens (at f/11.5), on nights of variable seeing. In this particular case, there was a jump in fwhm of more than 1" around the middle of the session. I suspect that masked-streaches and morphological reductions accentuate this effect. That being said, I don't dislike the outcome.
cheers
Ignacio