Annoyance: Sequencer Racks, Drag and Drop Plugins

setAutoScrollMargin(5), It seems to mitigate the problem almost entirely.

qtractorPluginListView.cpp line:331

// Construcctor.
qtractorPluginListView::qtractorPluginListView ( QWidget *pParent )
	: QListWidget(pParent), m_pPluginList(nullptr), m_pClickedItem(nullptr)
{
	// Drag-and-drop stuff.
	m_dragCursor  = DragNone;
	m_dragState   = DragNone;
	m_pDragItem   = nullptr;
	m_pDropItem   = nullptr;
	m_pRubberBand = nullptr;

	// Common tiny scrollbar style stuff.
	m_pTinyScrollBarStyle = nullptr;

	// To track the current item...
	m_pCurrentItem = nullptr;

//	QListWidget::setDragEnabled(true);
	QListWidget::setAcceptDrops(true);
	QListWidget::setDropIndicatorShown(true);
	QListWidget::setAutoScroll(true);
	QListWidget::setAutoScrollMargin(5); // <----- !!! Here

It's more accurate to drag upwards than downwards... but that's already happening.

It's clear that the strange behavior is due to the scroll function.

Note:
QListWidget::setAutoScroll(false);
This eliminates the problem and allows dragging up, but not down.

setAutoScrollMargin: It mitigates the problem, but does not solve it, it is unnecessary.

I have found a better solution, activating autoscroll only when necessary.
This seems to work.

line:356

	QListWidget::setMouseTracking(false);

line:1880

void qtractorPluginListView::dragMoveEvent ( QDragMoveEvent *pDragMoveEvent )
{

	if (canDropItem(pDragMoveEvent)) {
		if (!pDragMoveEvent->isAccepted()) {
			setAutoScroll(true); // <--- here
			pDragMoveEvent->setDropAction(Qt::MoveAction);
			pDragMoveEvent->accept();
		}
	} else {
		pDragMoveEvent->ignore();
	}
	setAutoScroll(false); // <--- here
}

The problem is caused by Qt's autoScroll functionality.

Therefore, I believe the best approach is to directly address this behavior. It also provides a bit more flexibility, or at least that's the impression I got after testing.

After testing, this is the configuration I'm most satisfied with, but of course, it's your decision.
Instead of disabling DragItem, try disabling or enabling autoScroll as I mentioned earlier:

	QListWidget::setAutoScroll(false);
	QListWidget::setAutoScrollMargin(4); // It adds more precision, so it's good to add it.

//	QListWidget::setMouseTracking(true);

void qtractorPluginListView::dragMoveEvent ( QDragMoveEvent *pDragMoveEvent )
{

	if (canDropItem(pDragMoveEvent)) {
		if (!pDragMoveEvent->isAccepted()) {
			setAutoScroll(true); // <--- here
			pDragMoveEvent->setDropAction(Qt::MoveAction);
			pDragMoveEvent->accept();
		}
	} else {
		pDragMoveEvent->ignore();
	}
	setAutoScroll(false); // <--- here
}

Thank you so much, whatever you decide, it was worth it in the end. One less thing to worry about :)