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You’ve seen it before - Exposé’s F-10 mode stops working for no apparent reason. F-9 is still good to go, but F-10 just looks busted.

Why?

Your application has set one of it’s NSWindow instances to the desktop level or lower (kCGDesktopIconWindowLevel or kCGDesktopWindowLevelKey are where it all seems to start).

Can I fix it?

Yes - fixing this problem is simple - either stop using windows at or below the desktop icon level, or add the following code to a window category or subclass in your project and execute the “clearExposeTags” method upon an active instance of your troublesome NSWindow. If you’re using CGSPrivate.h, you can just include the method without all the typedefs and externs.

typedef int CGSConnection;
typedef int CGSWindow;
typedef enum {
    CGSTagNone          = 0,        // No tags
    CGSTagExposeFade    = 0x0002,    // Fade out when Expose activates.
    CGSTagNoShadow      = 0x0008,    // No window shadow.
    CGSTagTransparent   = 0x0200,   // Transparent to mouse clicks.
    CGSTagSticky        = 0x0800,    // Appears on all workspaces.
} CGSWindowTag;
extern CGSConnection _CGSDefaultConnection(void);
extern CGError CGSClearWindowTags(const CGSConnection cid, const CGSWindow wid, CGSWindowTag *tags, int thirtyTwo);

- (OSStatus)clearExposeTags
{
    CGSConnection cid;
    CGSWindow wid;
    CGSWindowTag tags[2];
    
    wid = [self windowNumber];
    cid = _CGSDefaultConnection();
    tags[0] = 0x02;
    tags[1] = 0;
    return CGSClearWindowTags(cid, wid, tags, 32);
}