For users not used for Spark behavior it can get frustrating. When one minimizes roster window it goes to taskbar. And if a user then double clicks on systray icon the window won't go up, it just disappears in the taskbar and after another click appears, but again only in the taskbar - minimized. So one have to actually find that window in maybe cluttered taskbar and bring it up.
Will Dimmit proposed a somewhat different approach in his patch, but it should fix this problem. https://github.com/igniterealtime/Spark/pull/9