undeveloped dog skills

Question
About a year and a half ago, my husband and I adopted a 2-3 year old neutered male boxer mix from a shelter.  He appears to also have some pit bull in him.  Fenway a great dog but has some really strange dog interaction habits.  He is definitely a leash-aggressive dog (barking and lunging; we are currently working on that problem with consistent training and treats for calm behavior).  However, in the few instances when he has actually managed to come in contact with another dog on a leash, they just sniff and sometimes try to play.  Off-leash, he gives extremely mixed signals to other dogs, leaving everyone baffled.  For instance, when we are in an area with dogs who are off-leash (and he himself is off-leash), he runs like a bullet up to other dogs, sniffs, and then immediately seems to want to play.  He gives signals like play-bows, lying down, running in circles, and other non-dominant play-initiating stuff.  However, at the same time as he's doing all that, he may also be growling and barking in a threatening way and his neck/back hair is standing up.  If the dog decides to play with him, they seem to have a GREAT time, and it's usually clearly playing.  Occasionally it becomes unclear whether it's playing or whether one dog or the other actually means business, but it's always sort of on the line -- it's never an outright fight.  He has never hurt another dog, nor been hurt himself.  (Yesterday he and the other dog crashed into me and he accidentally grabbed my leg instead of the other dog; there was hardly any pressure at all - he was CLEARLY intending to play and not hurt.)  If a dog decides not to play with him, he totally disregards their signals to go away.  I don't know whether he doesn't understand the signals or whether he simply feels confident enough to intentionally ignore them.  This can sometime escalate into lots of quasi-aggressive barking (while simultaneously play-bowing...).  This usually makes the other dog's owner pretty uncomfortable (and understandibly so!).

I am pretty sure I'm correct in my observations - I know sometimes it can be tempting to see what you want to see and not what the dog is *actually* doing, but I do think my observations are objective.

I'm not sure how to handle this.  My questions are:
* What the heck is my dog thinking?  :)
* Is there a way we can help him learn dog social skills?  Rewarding good behavior with treats is an unlikely option because he doesn't like treats nearly as much as he likes playing with other dogs.  :)

Thank you for your help!

Answer
Well this actualy sounds like it is play-and he is probably young so he always wants to play! Sometimes older dogs don't want to be bothered,but two young dogs can really have fun,and 2-3 is still very young and alot of dogs don't calm down until they are around 6

And it seems like he has pretty good skills,the main problems dogs can have with each other is humping and it doesn't sound like your dog does that which is good

Sounds like you have a nice friendly dog-so enjoy him!