Well, this is my first Bug Report Friday. As an Apple bug reporter virgin, I'd just like to say this: Phew, I did it. This has the problem ID of 4416456.
Summary:
GarageBand will always minimise its main window when the user double clicks the title bar. It does this despite settings in the Appearance pane of System Preferences.
Steps to Reproduce:
1) Launch GarageBand and make a new project.
2) Double click on the title bar of the main window. The main window being the window with the wood-grain sides.
Expected Results:
The window comes to the foreground if in the background, or, nothing if already in the foreground.
Actual Results:
The window minimises to the dock.
Notes:
This does not occur to the windows in GarageBand using the `brushed-metal' theme, such as the Musical Typing window. It only occurs to the wood-grained main window.