Bug in custom attributes exposed by Ruby...

fizgig

Make a group and give it a custom attribute "TEST_1" equaling "abc" (value isn't important, the underscore in the var name is...)
Select the group and in the ruby box, type Sketchup.active_model.selection[0].set_attribute("dynamic_attributes","TEST_1","efg")
Now try to delete both custom attributes in the custom attribute dialog box.

Good luck! I've got some library components where I'm trying to delete these doubled attributes and I haven't figured out how yet. Not even the delete_attribute method appears to help.