I found a bug in the DHTMLX tree version (2.6). The problem also occurs in the sample on dhtmlx.com/docs/products/dht … g_ext.html
When you open “books” and then close “horror” (do not close “Dan Brown!”) and then drag and drop “Teens” between “Horror” and “Science Fiction & Fantasy” “teens” will appear as the first child of “Dan Brown” instead of between “Horror” and “Science Fiction & Fantasy”
The bug occurs because the code on line 2386 and/or 2398 at the dhtmlxtree source file checks if the specific node is hidden without taking into account if the parent of this item is hidden.