How to add existing resources to a container

Hello everybody!

I am involved in the Apache Marmotta Incubation proposal (http://wiki.apache.org/incubator/MarmottaProposal) and have 2 questions regarding the current working draft of October 25th.

On 5.2.1 it says a LDP Container is a LDP Resource.
On 4.4.1 it says on HTTP PUT it must replace the persistent state of a LDPR with the entity representation in the body.
On 5.5.1 it says, servers should not allow HTTP to update LDPC's members.

This is somehow inconsistent. As 'must' is stronger than 'should not' (in my opinion), 5.5.1 is redundant. Why is 5.5.1 necessary?
I even do not know how an existing LDPR can be added to a container without PUT (what should be possible somehow regarding 5.2.2).

Many thanks for your answers and best regards!
Thomas