The problems seems to appear more precisely and more often when using blender for a while without quitting the software.

I tried on my iMac with 1 GB Ati - with 2 windows on 1 screen, don't have 2 screens here. All goes fine then (you could try 1 monitor too btw).

You also should tell what kind of mac you use, and the monitor/screen resolutions.

I think you probably run out of graphics memory. Things you can do:
- Do not use Multisample (or set it to low value, like 2 or 4). Every multisample level allocates a full window worth of gpu memory
(note it needs restart of blender to take effect)
- Try to switch to another buffer swap method (user preferences, system tab, try draw method "overlap" or so)
(this has effect immediately).

Another issue could be a driver upgrade failure... I am still in 10.7 here btw.

I have noted the same issue, but as well only with 1 Screen: If you have two Blender Windows, change frontmost App to Mail or any other app by cmd+Tab and then back to Blender, Blender does not respond at all, unless i change Blender frontmost Window with cmd + <
This is very disruptive behavior in workflow...

I've noted: Happens on 2.64-2.66a+current SVN but not on 2.62 (Have no 2.63 at hand to test...)

osx 10.8.2, macbook pro 6.2, 8GB Ram, nvidia GT330M

No problem for me with Cmd-tabbing around. iMac 10.7 with ATI.

I do notice this weirdness when 1 window is in full screen mode though. Is that it? Apple fullscreen support is unknown for me though... its not very common to go fullscreen on a program, and then have the program again open a normal window.

I've added regular OSX full screen now, which does much nicer than our own.

How to redo what Jean-Christophe mentions I still don't understand.

Since i mainly work fullscreen and often have a second window open - it's as you said.

Now, i work a lot on two screens - and the apple fullscreen is totally useless in this case, since it blocks out the second screen.. while you can add a second blender window to the second screen, you can't have any other Window from another app there...

I say this cause i fear you want to remove the alt+f11 old fullscreen behaviour. And this cause: currently you can enter Apple fullscreen mode and then again with alt+f11, which then prevents apple fullscreen to be un-fullscreen. You can't exit fullscreen mode then. While this is probably a very rare case, i just wanted to tell you since i've noticed it. In my opinion you don't need to fix this behaviour.

i have noticed too: if you have two windows, say Main with 3d view, second user pref. If WIndow user pref is active and i alt+click into 3D View, it does respect the click - changes the 3d curser, but does not respect the alt. (The alt is for rotate View with Emulate 3 Button Mouse) - i think it is related to the issue from Jean-Christophe

Someone else told me about this useless apple-fullscreen for dual-monitor users. For single-monitor (especially laptops) it's very nice though.
So we just keep both :)

I can redo the issue with 1 monitor, but it's very hard to debug... will keep digging though.

Great.
To fix the initial Bug would be great too... it is annoying ;-)

I was away for a few days but I'm back :)

The latest fullscreen mode is very interesting and seems to have a really better behavior.

When the main blender is in fullscreen mode (the new OSX way that Ton implemented last week), the second windows opened with a "shift-click" can not be full screened the same way, but the cocoa windows can be maximized on the second screen without my initial problem of lost focus.

A interesting update could be the use of the second screen to display "internal" blender windows as an extended screen (I mean without the cocoa border. Final Cut Pro X and Motion do it rather well, even if you can not choose which windows you want on the second display).

I also noticed the problem described by Sebastian with the alt key problem. It is quite similar to my initial problem because you have to click on the second windows to get the OSX focus but, at least, the UI does not get fully locked.

Ton, you asked my about my hardware :

MacBook Pro 8.2 (late 2011)
ATI 6770m, 1Gb in 1680x1050 (15" HR Screen).
My external 21" screen is connected via Thunderbolt.

This is getting very confusing... I hooked up a 2nd monitor to the iMac, and I cannot redo any error whatsoever anymore. Not in current svn, nor in 2.66a.

1) The original report (dual monitor, 2 windows, save file, inactive) I can never redo, whatever I try. After every save (Cmd S) the UI remains responsive, in either window.
2) Sebastians report (dual windows, two times cmd-tab) also always works.

The ALT thing that got reported is entirely different. Blender's inactive windows are not getting events other than scrollwheel (trackpad pans) and mouse-moves.

I need precisely & reliable ways to redo errors consistently... it's something I can't get to understand yet.

No news? We're about 14 days before release :)

The "If you have two Blender Windows, change frontmost App to any other app by cmd+Tab and then back to Blender, Blender does not respond at all" appears only to happen if one of the Blender Windows if Fullscreen (alt+f11 Blender Fullscreen, not osx Fullscreen). Sorry for beeing so late - post release...

"The "If you have two Blender Windows, change frontmost App to any other app by cmd+Tab and then back to Blender, Blender does not respond at all" appears only to happen if one of the Blender Windows if Fullscreen (alt+f11 Blender Fullscreen, not osx Fullscreen). Sorry for beeing so late - post release..."

This issue is solved as it seems. But the initial Bug Issue, with two screens, still remains.
2.68.5 r60072M

That's quite an old report and quite few changes were made to blender in last year :)

Is it still an issue with latest builds form builder.blender.org and 2.72 testbuil1 ?