if you revert the postbit_legacy template you will lose the style edits made and will be left with a very basic looking postbit. My advice would be to avoid that course of action since you are clearly using a custom style.
Check postbit find the avatar code copy it and replace the avatar code in your postbit_legacy
Since the avatar shows in postbit but not in postbit_legacy I would first check that the two pieces of code are not disimilar. There will be some changes of course because of the location but the variables and the url for the avatar should remain the same not too sure there is a url actually think its just the avatar var but best to check it. Failing that contact the style makers because that style your using is not free so the very least they can do is supply it working in both version of postbit
