Target v2 Launch Extension Errors - mbox

Question on Target v2 extension - Migrating from v1 to v2, when I publish a library that removes v1 rules, and v2 rules fire I get one 200 POST and then a 400 POST with the console message:

 Errors: field - [execute.mboxes] - global mbox is not allowed in mboxes 

But if I run my Target v2 first and leave on the v1 rules, no error and v2 Rules run as expected... what is happening?