I'm almost INTx but I've had this a couple of times. I remember that it was always with other INTP's though. It's not really a conscious thing for me. I'm normally very introverted and don't talk to new people until I know what they're like, but I can talk to these people after five minutes. I've met a couple of them recently and it's surprising how fast we can get into a complex topic/argument.
For example: When I met my friend's roommate I was able to talk to him easily, and when his friend came in asking for homework help we all had a big discussion, which was something I would have avoided (subconsciously) if the guy had been, say, an SJ.
I click with people fairly regularly. I'm an INTP for the most part. It happened not long ago with an ENFP that I randomly met at a bar. He was standing nearby and we just started talking. Within a few minutes, I just knew this guy was freaking cool as hell and 3 monthes later we still talk. It's all a bit of an intense interaction. We talk about some pretty deep things that I'm not really used to getting into in the normal every day life. It's not really a romantic thing. We just see each other casually and enjoy each other's company.
I've had this happen in the past with other ENFP's and INFP's, and to some degree a couple of ENTJ's and ENTP's as well. For me, it might just be an N thing, or anyone for that matter that can delve into some deeper realms of conversation without getting freaked out.
Has anyone else seen a similar thing with clicking between INTP's and ENFP's?