Q: iMovie 2.2.3 automatically saves to camera roll when I don't want it to

I agree that it was super confusing for me as well.  I'm not sure I totally like that I have to delete clips that I captured (but didn't use), but then again, I guess it was the same before (they were just stored in the project which made them slightly easier to get at. 

-However- I will say the change is now growing on me as I just finished my latest project. Having the clips I captured in iMovie saved in my camera roll allowed me to easily edit them in another app (Overvideo - for adding custom titles). I even shared the clip itself to my friend who wanted it for a trailer she was making. After comparing the file size of the my project it doesn't seem to take up any additional space on my iPad either.  In any case, I know this doesn't address your issue, but just wanted to offer my 2cents so far.  Unfortunately I don't think there is away to turn that function off at this point.

Yep. I noticed that too, but I actually like it. So glad I no longer have to manually save each in-app captured clip to my camera roll by digging for each clip in my media bin... Also, I find it easier to transfer clips from my iPhone to my iPad because they are already in my Camera Roll and can find them easily.