Does anyone know how to stop Android deleting APNs when a new SIM is inserted?

I use a MVNO SIM so have to setup the APN manually. On inserting the SIM the phone automatically adds the APN for the parent network (O2 UK). I have to manually enter the correct settings for my provider (giffgaff).

This is fine until I take out my giffgaff SIM and use a different SIM in my Galaxy S3. Then the manually entered giffgaff APN is deleted and replaced with the APNs for the new SIM (T-Mobile). When I reinsert my giffgaff SIM it automatically creates APNs for O2 and I have to manually enter the giffgaff APN again.

Surely it doesn't need to delete existing APNs, why can't it just add new ones to the list, then I can choose the one I want.