Confused about Window GUI Issues

Hi,

I was having a closer look at applications I use everyday in order to get a better idea about what kind of windows are best suited for my own app. I was particularly interested in which windows should stay at the front, which should be toggled open/closed, etc. During this process I came across some behaviour that made me very confused about this whole issue, in spite of all the reading I've been doing on the subject. So I would appreciate it if anyone would care to comment on this:

Playing with Mail app's Window menu, I noticed the following:

1. Of the four "extra" windows in the application, two look and behave like document windows while two, namely, 'Address Panel' and 'Activity Viewer', look like floating or utility windows.

2. These last two look the same. Also, both have key equivalents on their corresponding command in the Window menu, and both are toggled open/closed by the menu command or key equivalent. However, 'Address Panel' stays above all windows while 'Activity Viewer' hides behind the other windows when these are brought to front. As a result, if the user forgets he has just coverred 'Activity Viewer' with, for example, the 'Message Viewer' and then uses the menu command to reach 'Activity Viewer' nothing, it seems, happens, unless he issues the command one more time, because the first time around Mail was closing it behind the scene.

3. While the above behaviour may be quickly learned (although still irritating), things get really strange when you have the Adress Panel and the Activity Viewer open.Then, if one is obscured by the other, and the user is not aware (maybe because its the first time he is using these features), trying to get to the Activity Viewer through the menu looks (to the user) completely broken, no matter how many times he clicks the menu or uses the key equivalent.

So I was wondering:

What is the rationale behind these diferences?

Why not show the window instead of closing it, if it is called while obscured by other windows?