Thanks Welder, I really like this handy carbine, too.
I'll check it out tonight once more, but didn't find anything special while cleaning it after range.
I don't really mind if it fires that way, it's kind of cool. Just would be nice to know what causes it and how to avoid it/make it so.
As I mentioned above, the former owner did modify the trigger, he welded a brass block on the trigger base, which forces it to be partially pulled back all the time. It makes the pull much shorter and faster. Not totally sure if the inner parts were further modified or not, but the trigger goes very smoothly and easily. I've always read that these carbines got hard and heavy triggers, so I guess this must have been modified strongly.
I guess asking Ruger for a new trigger (in case I don't like this) would be a waste of time, right? These have been discontinued long ago, there are no spareparts offered at their site.