Comment # 3 on bug 988593 from Tom���� Chv��tal

Ok then with xfce I unfortunately can't help you.

There is a bug in it how it handles the gtk configuration and it causes quite
few gtk3 apps to hang and render incorrectly.

Fix for you is to uninstall the libreoffice-gtk3 and stick with gtk2 version
that comes from libreoffice-gnome subpackage.