Menus, fields and not activating a mouseUp?

[David Bovill]

You have a field with a contextual menu - so when you control-click on the
field a popup menu apears (called in a mouseDown handler). If you do not use
the control key - but simply click the mouseUp handler does something
else...

So how do you prevent the mouseUp handler? Neither exit to top nor the
pending messages seem to help... so I have always set a flag in the menu
code and then checked this in the mouseUp code... still is there a better
way to prevent mouseUp messages from being sent?