I think this has happened to me only in VP15 (never worked in 14, don't remember it happening previously). Sometimes, double clicking just stops working. Sometimes it's just within an instance of VP (and still works in another). Sometimes it will work in one until I paste in a text event or something else from an instance where it has stopped working. Sometimes I have to reboot the whole system.
It's similar to that bug in AE where double clicking on comps stops opening them up and you have to close out or even reboot.
Is this happening to anyone else? Is it a known bug? Obviously right-clicking is the solution in a pinch, but some things in VP don't have an open or add option when you right click - like editing text in Protype Titler - and you just can't change certian things without closing out or rebooting altogether.