The "scales" skin was started around r348891 2005-11-25 as a copy of the "pelt" skin.
When adding enhancements to the pelt skin we have tried to also add them to "scales", but it seems to be out of synchronisation now. It would be good to consolidate, and would also mean that we have less to maintain.
Apart from the "showonlywhenselected" menu enhancement, i am not sure if anything else was added to Forrest. (Perhaps Ferdinand has some other local changes that could be committed.)
The following are some of the email discussions around that time. These also discuss some potential enhancements, and even provide some code examples.
Subject: Menu Overhead Problem (and an offer to fix it)
Subject: Scales Skin added to head
Subject: Additional features in scales-skin
That  also links to issue FOR-91
(flat navigation) which has some other ideas and links to mail discussion at http://marc.info/?t=107007134500002