It looks like that handle should be able to pull straight off the end of the shaft once you remove the screw. See this exploded parts view:
http://www.makita.com/en-us/Assets/images/Products/_PartsBreakdowns/PB_2703.pdf
My experience with them is that people tend to get frustrated and abandon the lock lever and just run the saw "loose". Scary as it sounds, I've seen it on more than one site.
Anyway, I don't have a fix for you if you can't get the handle off to re-position it.
Makita does have a tech support line if you want to give it a try. Otherwise, you may have to shell out a few bucks to one of their service centers. We used to have a great one in Albuquerque, but it's now defunct. People don't seem to repair tools like they used to...
Locate Nearest Service Center online
or Free technical support center (1-800-4MAKITA)
Monday – Friday 7:00am – 7:00pm EST
Good luck, and best wishes...