I noticed that when I drag an element once, release it and then drag it again,
the icon showing if drop is allowed ('dropAllowed' or 'dropNotAllowed' cls) is

This can be viewed in the drag and drop from grid to grid example. In that
example, dragging one record causes this problem to happen for all the rows.

In my code, where I have many separate drag sources and drop targets, this
happens per drag source: dragging an element that is a drag source causes this
to happen for that element on the next drag, but other elements that haven't
been dragged yet do not show this.