UPDATE w/ Possible Solution!
ok so I think i may have figured out a way to fix (or prevent) this bug from occurring; wanted to share. while i still haven't found the absolute cause of the problem i have found that if i let the screen time out while it's rotated horizontally it will stay like that until returning to the home screen, or any app that requires the vertical orientation. this then causes the auto-rotate to not work until rebooting the phone (POWER + VOL DOWN button). if you let the screen time out while it's vertical this doesn't seem to happen, and the auto-rotate will work fine. just a theory but so far so good, i've been trying to make sure to return to the home screen, or anything else using the regular orientation, before letting the screen time out.