Steps to reproduce:

1) Create a read-only folder in Drive
2) Open a team drives folder
3) Drag a file from a Team Drive over the Drive folder until it expands, and then over the read-only folder

Expected:
The read only folder does is not allowed as a drop target.

Actual:
The read only folder can be dropped onto.

This is a fairly nuanced corner-case, but happens because of the way drag-drop is implemented. Re-writing the drag-drop controller properly, with redux and polymer, will fix these cache state issues.