You know, that pretty much sums up the whole thread.
Seriously, what do you CARE what that person’s name is short for, what you can shorten it to, or what you’d rather call them? Is it your name? No? Then seriously, minimal politeness would suggest you call them by their chosen name.
Yes, but as a lot of posters (and myself) have probably come to conclude, a lot of people don’t possess minimal politeness. Either that, or they’re as absent minded as a brick of cheese!