Deleting grass layer cause character to display above "v" tiles instead of behind

[lulalala]

It seems when grass layer is deleted, character would be displayed on above tiles which it shouldn't (e.g. house roofs, top of trees).

(However I can only reproduce it from my own tmx file)

** Update **

I think this has something to do withnbGroundLayers being 4. I changed it to 1 (to suit my need) and things works now. Not sure how to properly fix this though. I don't see a similar 4 in browserQuest source code. Why is it necessary here?