The "#event properties" doesn't show properties if they override a parent's object property.
Looking at the object's .yy file, we can the "properties" are being properly parsed as shown in this example :
But in the event of properties who override a parent's property value (the "overriddenProperties" array in the .yy), the properties do not show up in GMEdit, as shown in this example :
The problem occurs when using the latest beta version (and prior versions too, but I'm not sure which on I was using at that time).