I am not sure I understand what exactly you are asking. Can you please elaborate a bit more?
What do you mean by "deactivate the "collapsable behaviour" when i drag over source's item neighbour "? Is it that you don't want a collapsed item to expand when you drag over it?
Regarding the "TextDropBefore", "TextDropAfter", "TextDropIn" properties - if you do not want to see the default text, you can simply set these properties to empty strings.
Also, I am not sure I unserstand your last question. Do you want to forbid dropping in the left treeview?
Please explain a bit more thouroughly and I will be happy to answer.
the Telerik team