Wondering if this is a bug somewhere in onmousedown, in 4.1.0f4. In the latest version of our project onmousedown suddenly stopped working. Found a backup a version where it works, brought that project up to our latest code version, it continued to work. 30 mins later the same problem, onmousedown stops firing. Go back to the backup project that was working and onmousedown now does not work in that any more either.
Here is a trick that fixed my issue with mouse down events not being received by certain game objects:
Delete whatever camera object is used to view and event listen your game objects in question, then re-add it to the scene. For whatever reason, it worked for me.