Xfce Synaptics Touchpad Scroll

Just installed Xfce and using the Synaptics Touchpad for an Acer Aspire Laptop

mouse works
tap on touchpad works for click
scroll not working

something strange: if I make contact with the left side of the touchpad, I can scroll a few lines with the right side

but then it jumps to the top and bottom
no control

any ideas

thanks in advance