There is a known bug with the flag and pushpin type symbols, where the anchor point of the symbol is the bottom of the symbol, instead of the center. These symbols are not positioned correctly. The fix is scheduled for our next release in March. Until then, it's best to stick with symbols that are centered on their location (like circles).
I'm not sure why you can't change symbols at times. I'm not seeing this. Please let us know if you have a consistently reproducible case.
Thanks,
Mike