Maybe somebody has played a little joke on you by finding the image that it uses and editing it to be upside-down. Does anyone else have access to your computer?
Or actually, FL studio.
OP: Are any other images which would be built into the OS upside down, i.e. application icons, other icons in syspref, etc?
Or it could be you playing a cute joke on us
Printer in the kitchen?
[bad joke]did you switched language settings to Australia ? Down under ? [/bad joke]
[bad joke]the prototype of the new batMac[/bad joke]
More sirious: did you installed any different graphic driver ? E.g. to drive external screen via USB ?
Did you played with tools from XCode changing settings in the graphical subsystem ? Some times I had some funny effects on my iPad.
Anywhere else in the system ?