For a CMT bean, if the transaction attribute is NotSupported or Never, the method executes with an unspecified transaction context. In the case of the Supports attribute, this happens only when the client calls without a transaction context.
I believe that it's the opposit, in NotSupported or Never case, the method executes without a transaction context, and in the case of supports attribute, the method executes with unspecified transaction context. Correct me if I am wrong.