Error: Decorating class property failed. Please ensure that proposal-class-properties is enabled and runs after the decorators transform.

This error occurs when I'm consuming a V2 addon that has not complied _away_ class properties.

This is incorrect behavior, because
- my browsertargets all support class properties
- the _app_ has proposal-class-properties, so it should use that
- how does this end up working for regular v2 packages? have we always not been able to use class properties?

Is there a way to tell ember-cli-babel to ignore v2 addons? or maybe only run "if it needs to"?
I guess maybe a core_er_ issue is that ember-cli-babel is incorrectly determining that it needs to run on the v2 addons?