According to the spec
https://docs.oracle.com/javase/7/docs/api/java/awt/dnd/DragSourceDragEvent.html

The Ctrl+Click should cause ACTION_COPY action but in fact, ACTION_NONE is occurred during the drop.

We have a few tests for this functionality:
java/awt/dnd/CustomDragCursorTest/CustomDragCursorTest.html
java/awt/dnd/DnDCursorCrashTest/DnDCursorCrashTest.html
java/awt/dnd/DnDRemoveFocusOwnerCrashTest/DnDRemoveFocusOwnerCrashTest.html
java/awt/dnd/DragExitBeforeDropTest/DragExitBeforeDropTest.html
java/awt/dnd/DroppingVMCrashTest/DroppingVMCrashTest.html

But unfortunately, all of them pass on macOS due to bug in the robot, which skips the pressing Ctrl and run DnD just by mouse.