Why is SMS reply number different from MMS reply number in Marshmellow?

[AC Question]

I have a Moto X 2014 updated to Marshmallow. I live between the US and New Zealand and change SIM cards between the two (T-Mobile and 2 Degrees). Everything was working fine for the last year until I upgraded to Marshmallow in the US then traveled to NZ one week ago and changed to my 2 Degrees SIM card. Now when I send a SMS text to the US (texts within NZ work fine) the reply number shows as +16421751950 since 64 is the NZ's country code when someone replies to my text their text goes to a non-existent US number given the the added 1. What is very strange to me is if I attach a picture to my message making it a MMS the reply number shows as the correct +6421751950 and the person receiving the MMS can reply to me and I will get their text. I have double checked APNs and used both the default app Messaging and Next SMS with no different results. Hopefully someone could give me a suggestion as to what to try next.