There is an interesting bad interaction between my drag-and-drop code and Rubric. It kills all Rubric editors at the same time, so it looks to me like a problem with the Rubric background thread interacting with mouseMove or mouseEnter/Leave. https://vimeo.com/139353992 To reproduce, Load DragPanels from StephanEggermont/DragPanels and NewUI from StephanEggermont/Documentation In a Playground open a panel CodePanel new openInWindowLabeled:'Code Panel' add a few cards (drop them in the panel) (CodeCard class: CodeCard selector: #initialize) openInHand and expand them by clicking on the arrow Right click on the empty area in the CodePanel and open the colors. A fast drag from the color panel to the rubric area of the code card sometimes results in the rubric editors losing their content. Stephan