I have the same problem with Safari tabs looking the same, menus flashing and in fact the L6 mouse acted as if the left click was on full time. All this happened only when booted into 64 bit. I'm on 10.6.1 Macbook Pro 17" early 2008. I tried to email Logitech but their mail has been down temporarily for a while so I'll put it here instead.
Everything works properly when booted into 32 bit.
While testing in 64 bit I had my mac wireless mouse working properly and the Logitech mouse acting up. I have replaced the driver with USB Overdrive and all is well in 64 bit-land
Logitech Control Center
For their USB mice & keyboards.
Version: 3.1