Lost in Space(s)

I have various Apps set up in spaces: Finder in (1), DTP progs in (2), Mail in (3) and Browser in (4). Sometimes when I'm using an app with an open document I switch to finder or mail... then when I switch back the app is there, but the open document has disappeared.

The App tell's me the window is open but I cannot bring it up, I have to quit the App then re-open to bring the document up again.

Is this an official bug?