This is an AfterEffects thread, but it lists some issues with event handlers that I think apply here as well. I don't have CC, but I changed my addEventHandlers("click") to onClick and I haven't had any complaints from CC users. The thread (and the threads it links to) might have more detailed information to suit your case.
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, thank you for this pdf. It enlights quite a lot of things.