help - multiple parts selecting

Hi,

Having a bit of an issue that probably someone knows the answer to:
When I click to select a part in the arrange window, cubase now selects all of the parts in a vertical line with that part - like they are somehow grouped…

I must have pressed something - how do i turn this behaviour off, so a click on a part selects only it?

thanks

This seems to be a bug… I can find no way of fixing it…