Version: (using KDE KDE 3.5.3)
Installed from: Debian testing/unstable Packages
If a window is shaded and then minimized, it does not appear on the taskbar. Effectively, it simply vanishes when iconified. The only way to see them again, is by turning off the "show only minimized buttons" option.
I am not sure if this effects any other minimized windows, although I did test "maximized" windows and they are fine.
*** This bug has been marked as a duplicate of 81271 ***