This doesn't annoy me immensely, but I don't like it very much.
I have a bunch of not very close relatives, cousins, their wives or husbands, their kids and grandkids who IMO mangle their names.
You used to often hear of couples who gave their newborns names that couldn't be shortened, well this bunch broke all the rules.
There is a Kelly, who is always called Kel, a Charlie called Char, a Warren called Wal, which I always thought was short for Walter, and a Zöe, which I think is a nice name, but she is called Zö.
There is a husband and wife friend of all of them named Albert and Debra, they are known as Albs and Debs.
Conversely, in among them is a William, and his parents have made it crystal clear that he must always be known as William, never Will, nor Bill.
Some of them used to call me Tone, but eventually got the message when I consistently blanked them, Tony is okay, as is Anthony, but not Tone.