Mechanical System Design .... new UI &Sub-mecanism

Hi, 
I'm using Mechanical System Design with the new UI (Mechanism like Motion Design).
i have the mechanism "mec_verin" and it's impossible to add it as a sub mechanism of "mec_SE_Bras_verin".
Any idea?

With previous Ui it was easier to add sub mechanism with "assembly mechanism" ... with the new one, do i have to add and seelct each one ?