NFS can't write files when retention active

I thought with retention, you can post new files but when deleted they don't disappear until the retention period has expired... is that right?

Whenever I have retention enabled on a bucket and I try writing files to it over NFS, I get:

tar: IMG_5672.jpg: Cannot open: Read-only file system

tar: Exiting with failure status due to previous errors

Remove the retention setting from the bucket, and it works fine (it errors because tar is trying to change ownership, but I understand why that's an error in this context).