Hi Italo,
Ideally this should not happen. Even if your procedure is acquiring locks on the tables being modified in the procedure, other sessions should be able to query those tables with simple select operation. Since you mentioned that the other session resumes after the procedure is cancelled, it looks more like locks waiting in the session.
I am not sure if something is logged in the trace files or not.
May be, you can open OSS message for this and let SAP look into this.
Fortunately (or unfortunately) I did not experience such behavior till now. 
Regards,
Ravi