strangely, MorphOS renders Icons "not visible" if I go and "fix/snapshot" a certain window (!)
If I do, the Icon for USB-stick and Work-disk partition are gone (and this stays even after a re-boot!)

Only solution was, to delete the still existing "disk.info" on these devices and copy over new ones.
Then both are back on Ambient desktop....

I changed the original MorphOS icons - I am using OS 4.1 glow-icons as replacements for "harddisk" and "USB"

kind of strange behavior, I guess