When there is text in the clipboard and one paste the text in the tree pane, a new document is created with the text in the clipboard and with the first line as title.
I used this feature in the past to split a long document in various documents. I was doing this by cutting the text with ctrl-X then going to tree pane and pressing ctrl-V. This no longer works.
Note: copying with ctrl-C then pasting in tree pane with ctrl-V still works.