FWIW, I have used Mig gas with the TIG to get out of trouble when I ran out of Argon, it welds OK, other than it firing sparks like a fuse of dynamite.
Never had any increase in tungsten burn back. A little more instability in Arc, but nothing to worry about
My thoughts would be AC Balance is set to much for DC or polarity, Although Neil has mentioned he has used it previously without issue.