Problem with setting some _NET_WM_STATE properties in XFCE

[John Found]

Recently, writing some XLib GUI programs, I tried to set _NET_WM_STATE property of my windows to _NET_WM_STATE_ABOVE and _NET_WM_STATE_MODAL. But these values can not be set at all, using XChangeProperty function. 

Using xprop utility the values can be set, but they have no effect at all.

Another property value _NET_WM_STATE_SKIP_TASKBAR can be set and works, but only until the first minimization of the window. Then this value is cleared from the property and the window reappear in the task bar.

I tested the code with KWin window manager (on top of XFCE) and everything works as described in the specifications.

So, is this behavior a feature or a bug?

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John Found <johnfound at asm32.info>