Possible VirtualBox bug, seen on two different guest machines.
After I create a read-only shared folder on the host, I am unable to edit the share or rename it so that I can write to the selected folder from a guest. Something in the VM appears to be stuck on the read-only share definition, and that definition prevents me from creating new shared folders with the same name. Any new share with the same name continues to be read only. If I create a new R/W share with a new name it works fine, problem only seems to happen when attempting to reuse the name of an originally read-only shared folder for read/write.