Your replication target will remain read-only while it is still part of a replication context.

This is not specific to collection replication but also Mtree and directory replication too.

It is as designed rather than an error.

Regards, Jonathan

1. Collection Replication is one of methods used to replicate data between two Data Domain Systems. Collection Replication maintains the entire Source DDR /backup directory hierarchy on the destination DDR. Data transfer occurs as containers are created or modified.Once Collection Replication is established, the destination DDR remains in read-only mode until the replication is broken.

I'm no DD expert but this one looks relevant

https://emc--c.na5.visual.force.com/apex/KB_HowTo?id=kA0700000004S19

told you....I'm no expert on DD....Thanks Jonathan