Created attachment 116082 [details]
Some windows are transparent (most of them partly and transparency occurs randomly). For exapmle window "Insert - Indexes and Tables"
LO Last beta. Linux 17.1 XFCE Using compton compositor -backend glx -vsync opengl. Without compositor still transparent...
Yan: for the time being you can workaround the bug by starting LibreOffice with the environmental variable SAL_USE_VCLPLUGIN=gen.
Thanks for your report!
*** This bug has been marked as a duplicate of bug 91394 ***