I use fbpanel with fluxbox, I don't know if the bug may be reproduced with other window managers.
When a window is iconified, the corresponding taskbar item is shown with square brackets around the window title.
This is good, since it makes detecting iconified window taskbar items easier, whenever there are a number of identically titled windows in the workspace.
However, this does not happen with "sticky" windows (I mean: windows that are present in every workspace, rather than in only one). For iconified "sticky" windows, no square brackets are shown around the title in the taskbar item.
This is unpractical and should be fixed: "sticky" windows should get brackets like "normal" windows do, when they are iconified.