Hi Filip,
In CC the regular mouse event loop (mouseover/mousedown/mouseup/click) is interrupted and/or broken at some stage, leading to many many issues depending on the OS and/or the target widget. The AfterEffects thread that cchimi mentions has a lot of useful tricks and reports. In addition you might want to give a look at http://www.indiscripts.com/blog/public/ScriptUIEvents.pdf
In most cases mousedown still works, except for EditText(Win)—not to mention those crazy buttons and listboxes where RIGHT-click plays the role of LEFT-click
@+
Marc