May your issue is related to this :
https://github.com/fabric/fabric/issues/1392
Code Related Pointer :
load fabfile function:
find fabfile:
Not been able to figure out how option get parse and if --config is getting preceance over --fabfile or not...
My guess is that --config may get call after --fabfile option so --fabfile file passed get override by .fabricrc specified fabfile
If it's the case someone fixing this should write a test to make sure this bug is not coming back...
Also, I notice that I replyed to but I intent to reply to the mailing-list, but it goes to you personnaly because gmail reply button behavior seems to have change (before it was replying all by default, which was a feature to me)... I may make you think that I will solve your issue but I am not a fabric dev... I just want to make sure that someone trying to help you get the right information to do so, and version is really important.
Hope you will get more help, this mailing-list is strangely silent or maybe you can address your issue your self with the pointer above.
Richard