Layers, as I finaly figured out, are very usefull. We just should clear it up a little bit.
First:
Steve, it seems that the "0" layer has kind of a "higher priority" by default, always. When you hide that layer, in the material bar, the matterials ( visuals , spheres ) don't show, you can see the names only ( pic.1 ).
Also there's something with the primitive (the Mesh Primitive - see "a mesh" - is fine) created on an empty layer set as default, different than "0". The "0" layer pops up, although other was set as default. When you double click on the primitive and then close ( only by "Ok" ) the parameter window the "0" layer turn off and the ( say ) "1" gets active with the underline under it ( the same result can be achieved by simply converting the primitive into a mesh )( pic.2). Note: when creating two or more primitives without changing the settings, first gets active the " 0 " layer ( first primitive ) and then as an addition the default ( if different than " 0 " ).
Now, very important, about grouping- ungrouping. Ofcourse very important others opinion, how they generaly go around with it.
1)When
grouping items of the same layer, it's obvious
the group should stay in that same layer (
period) Ungrouping items, that originaly were located on the same layer, should be relocated on that " old" layer and not transfered automaticaly to the "default" layer
2) About grouping items from different layers: first I thought it would be good to prohibit that possibility and to mention, by a pop up window ( So'd just you know window

), that items can be grouped only when they belong to the same layer and they must be manualy transfered to the same layer before you can group them. Then, ofcourse I understood that it would be stupid, because you loose the ability to group at once a lot ( million ? ) of items without the need to manualy ( !!! ) edit their settings !!! So, grouping items, that originaly belong to different layers should locate the newly created group into
the default layer.
And here I bring up again the suggestion, if it is at all possible, to set the " default " layer via the Midle Mouse Button on the tool bar directly. You just click ( MMB ) on the layer you are currrently working in ( better maybe "working layer " - as a replacement to that " default" ), that layer gets the underline and everything you group will be transfered to that " working" layer. It's the way actually things work now, just you have to go all the time through the
Options menu, wich is not practical. Currently, when ungrouping items that originaly were located in different layers, each item returns to its original layer and that's the correct way, nothing should be changed, because when editting often you need to group things just for a sec or two and then relocate everything back. The only thing is that grouping items from different layers, as you mentioned, hidding the layer (of the item originaly ) hides the item inside the group. That should not happen. The visibility of the group should relay only on the layer that the group belongs. Anim8or should " seek " for the group layer's visibility only and only when items will be ungrouped they can be affected by their original layers.