If an opaque DragImageComponent is used (one that returns true from IsOpaque(), which happens on systems without transparent window support or if manually set), drop targets do not see the drop enter / drop exit messages.
The reason is that the DragImageComponent ‘sees itself’ during DragImageComponent::findTarget. In other words, it is finding its own HWND. The chain of calls is as follows:
hit = Desktop::getInstance().findComponentAt (screenX, screenY);
Component::getComponentAt()
Component::contains()
Win32ComponentPeer::contains()
in Win32ComponentPeer::contains(), WindowFromPoint returns the HWND of the DragImageComponent heavyweight peer, rather than the HWND behind it.
If the DragImageComponent HWND has the layered style set (for transparency) as a consequence of having returned false for IsOpaque(), WindowFromPoint does not find it in the call chain above and instead correctly finds the HWND behind the image window being dragged.