selection highlighting disabled by mouse right button

[pieren]

With the new mouse events handling, I get the following disturbing bug:

• select some objects on the screen e.g. with "find highway"
• all elements with the tag 'highway' are highlighted
• use the right button mouse to move the current view

If the mouse pointer is not on top of a highlighted element, everything is fine as usual.

If the mouse point is over one of the highlighted element, this element is seleted although we use the right button of the mouse and this diselects all other elements of course.