My iPhone's name keep getting "(2)" appended

I thought this particular problem was restricted to my Macbook & Mac Mini, but now it happens on my phone too.

I'm running iOS 8.3 on an iPhone 5S.

A while ago the name of my phone keeps getting "(2)" appended to the end of it (just like my Mac computers). So currently my phone's name is "Davids iPhone (2)".

There are no other phones in my house that have the same name.

If I remove the "(2)" from the name in the General / About / Name settings, it stays that way for a little while but eventually the "(2)" comes back.

I've tried changing the name in iTunes on my Macbook Air, but it doesn't change the phone (although it stays that way in iTunes).

I've also tried changing the name in iTunes and restoring the phone from backup, but that doesn't help.

I've also tried resetting all the settings with no luck.

The one thing I have noticed that might be relevant is that on both my Mac's and the iPhone I ran public beta OS's. All three are running production OS's now.

Any suggestions?

david