Greetings,
In the current version (2019 Q1) the expand Icon of the treeview node is being reset, if another node is dropped above it. To reproduce this behaviour you can take the Drag and Drop demo of the treeview. In the inital state the "Furniture" node is expanded. If you take the "Decor" node and drop it above the furniture node, the "Furniture" node stays expanded but the icon changes to collapsed.