Quite a few people have contacted me and there are others on other sites (including Apple’s discussion forums) have been complaining that APN Settings for Hotspots don’t save when changed. (Thats if you can edit them in the first place)
This is not across all carriers/countries/users as far as I know (It works for me for example) so it may be determied by what carrier you are using or other factors
I am sure Apple will resolve this “issue” maybe in the next update but at the moment there is really nothing people can do.
I just wished that Apple allowed people to set this Hotspot setting (and MMS as well) in profiles like I do with Data APN Settings.
Update: It seems this issue is affecting people who are using Carriers which don’t have builtin settings within the iPhone (Thus using the generic/default carrier settings). (Or I may be wrong)