Before going into exactly what is failing I have to first ask the question whether this is supported. If a user upgrades to 1.7 and then downgrade to 1.6, should things still work? I would say yes they should as that has always seemed to work in the past. With 1.7 I'm getting errors now. Basically after reverting back to 1.6 I get errors like:

time="2015-06-03T07:43:11Z" level=fatal msg="reflect: call of reflect.Value.Type on zero Value"