[Design] Selection behavior when choosing different collections

[Jeffrey Harris]

Hi Folks,

Currently, we're maintaining selection state for every combination of
sidebar collections.  This means that if you select a few items in
collection Astronauts, then switch to collection Butterflies, select a
few items, and come back Astronauts, your old selection in Astronauts
returns for your fun and enjoyment.

Things get interesting when you throw overlaid calendars into the mix.
Different selection state is persisted for the union of Astronauts and
Butterflies (hereinafter known as Butternauts) than for either by
themselves.

For bug 5613 (https://bugzilla.osafoundation.org/show_bug.cgi?id=5613),
I implemented behavior so that, when viewing Butternauts (with both
Astronauts and Butterflies overlaid), if you change from
Astronauts-on-top to Butterflies-on-top, any items only appearing in
Astronauts are removed from the selection.

I foresee confusion on the part of our dear users regarding this variety
in selection.  I know it confuses me that if both Astronauts and
Butterflies are overlaid, selection is (now only partially) preserved as
I switch back and forth between making Astronauts or Butterflies on-top,
but if I click on the Spelunkers collection, I get a whole new selection
state.

It's nice that selection is preserved between Chandler sessions, and
between Calendar view sessions.  I'm not exactly sure what would be
better than the current state of affairs.  I just wanted to point out
that the current situation seems a little odd.

Sincerely,
Jeffrey