| The reason you've probably had problems with the specialist after going back to Mixtard is because basic science says it's a phenomenally bad idea.
Look, I get that you find it a pain to have to inject every time you eat but you're not gambling by going onto Mixtard - the end result is guaranteed. Mixtard is a mainstream insulin in the same way that L-plates and stabalisers are mainstream. It's a good insulin for people who are getting used to the idea of injections but for long-term treatment it's not a good option. If you get an A1C under 9 with Mixtard then you're doing extremely well, all things considered. Although in terms of your health, you're still doing badly.
Having said that...
...your specialists have to juggle very carefully what's best for your health and what's best for your lifestyle. Like yourself I've regressed back with insulins - I went back from Lantus to Insulatard. However my specialist recognised that this was in my best interests because of the bad side-effects Lantus was having on my psychological health. They were also perfectly willing for me to try Levemir when it first came out, and when it turned out I was one of the few people it doesn't work for, I was straight back on Insulatard.
Now I'm back on Lantus because Insulatard was starting to destroy my life by making me have up to 9 hypos a day. In fact my specialist didn't really want me going back on Lantus (because of my history on it) but in the end we both agreed that in terms of my health and my lifestyle, Lantus was the lesser of the two evils.
The problem is that your specialist is tied down by their job. Their job isn't to give you what you want; their job is to keep your healthy. Doubtless your specialist cannot see any practical health benefits from you going back to Mixtard. That's why they're being difficult - you're asking them to violate the 4th item of the Declaration of Geneva, 'The health of my patient will be my first consideration'.
The GMC also have similar rules - 'make the care of your patient your first concern' and also 'respect the rights of patients to be fully involved in decisions about their care', which is the reason why you've been allowed back on Mixtard.  | 
