[mac wired mouse] button order seems to change from left to right and back!

I’ve managed to install opensuse 12.1 on an iMac 17" late
2006 model with the 64 bit distro and almost everything
seems to be OK.

However, I’m experiencing mouse problems that can be best
described as the button order changing without user intervention.
I’ve got the mouse button order set to left button but I’m getting
the right button sub-menu displayed and then it changes back to
normal left button operation.

Is there another option clashing or is it likely to be a bug?