Well at least Adobe is consistent. The Flash Installer is awful on OS X as well. For example, say you've disabled the translucent menu bar - you'll notice it's drawn translucent when the Flash Installer is the foreground app. (Nevermind the fact that the installer is a just an annoying wrapper around the OS X installer that seems to do nothing more than force you to quit your open browsers before it will continue. With some digging you can actually find where it's downloaded the real installer pkg, double-click that pkg to install it, then quit the wrapper.)
Is the Flash installer running as a different user? Menu bar translucency can be set per-user and translucent is the default, so if, e.g., you run an OS X GUI app as root using sudo, and haven't disabled translucency for root, you'll see this behavior.
Well at least Adobe is consistent. The Flash Installer is awful on OS X as well. For example, say you've disabled the translucent menu bar - you'll notice it's drawn translucent when the Flash Installer is the foreground app. (Nevermind the fact that the installer is a just an annoying wrapper around the OS X installer that seems to do nothing more than force you to quit your open browsers before it will continue. With some digging you can actually find where it's downloaded the real installer pkg, double-click that pkg to install it, then quit the wrapper.)