Item Numbering Schemes (ProductStream)

[rankinrj]

Noticed this in PS4.5 and get it again in 5.

When I create a new item numbering scheme, i like to test it a little before rolling it out.

so I right click am iam and assign an item. the default scheme is "Mapped" so I then RMB the top file and select change item number. However, at this point i realise that i made a mistake so do not click OK, but Cancel and go back to the Item Numbering Editor. I then move my I.N.S. from right to left to make it inactive but i cannot edit it or delete it. I have to create a new one and start from scratch.

in fact the only INS that I can edit is the "mapped" scheme and that is actually active.

How come???

What am I doing wrong??