I see one thing with 'reload':
For example I have some data in my combotree, and several items already checked (I have checkboxes).
If I reload data and new data extands existing data then it looks really great. What was selected - remains selected and I don't need to select it again as I do when I change URL.
But, if I reload data and new data does not include records that I have initially selected then old records remain selected.
Also, as old data is not available in combotree I see "ID"s for old records.
Can EasyUI self check this situation and deselect unavailable items?
In this case 
onChange event will work as I expect without extra magic from my side 
