After running program from terminal there appears this message.
Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
I don't know what is its importance but it's for your knowledge.
Thank you! I know about this, I don't know how to fix it and it does not hurt (I did not search the internet for a fix).
Because you use Qt library, I suppose the problem lies between Qt and Gtk rather than between Application and Qt and possibly has no serious impact on FET.
Yes.