Refresh NSImageView while NSWindow is being dragged around

Question

I've got a NSTimer which fires every few milliseconds to load and then assign a new image into a NSImageView. The NSTimer has been setup using various run loops (NSRunLoopCommonModes, NSModalPanelRunLoopMode, NSEventTrackingRunLoopMode) just so that it continues to do what it's doing when events are firing.

This works great however this ceases to work when the actual window is being dragged around the screen. I have confirmed that the timer is in fact firing during the drag, and the image is being assigned to the NSImageView as well. The only problem is that the screen contents don't refresh for some reason when the window is being dragged. This is possibly a built-in optimization but I'd like to disable this so that the imageview continues to refresh and re-draw even when the window is being dragged around.

I've tried the following inside the NSTimer firing block but this still did not force the contents of the NSImageView to be refreshed and redrawn:

- (void)animateTimerFired:(NSTimer *)aTimer {
    // .... load imageObj

    // set image
    [imgBackgroundView setImage: imageObj];

    // try and refresh the window forcibly 
    [[imgBackgroundView window] viewsNeedDisplay];
    [[imgBackgroundView window] display];
    [[imgBackgroundView window] update];
    [[imgBackgroundView window] flushWindow];
}

Is there any way to disable this 'optimization'?