Libre Office calc has now decided when a cell is selected it only selects the row and column headers you can still input but the cell is not highlighted. I remembered the thread about slow Firefox being caused by Debian now using modesetting DDX instead of intel-DDX ( why ?) and tried Towo solution of make an /etc/X11/xorg.conf.d/20-intel.conf which seems to have fixed it.
Section "Device"
Identifier "My GPU"
Driver "intel"
EndSection
That is worth a bugreport.
greetz
devil