This is a bug related to http://www.scirra.com/forum/array-values-not-being-set_topic53695.html?KW=array+properties where @Ashley sad that it could be happened only if a layout has been deleted.
If you create a new array when an event sheet is on focus in the editor, the array do not have properties - maybe the hidden instance is not created.
But if you have a any layout on focus in the editor it have the properties.
Could you solve this bug please!?