in our software build in qt 4.8.5 in some cases the drag and drop stops working. There are two places where it should work. One when dragging a file to a certain spot at the application and a second in a QTreeWidget where you can put some leafs into folders.
But on some machines (Windows) both methods just stop working or are not working from the start. Then only a forbidden cursor appears. After a restart of the application drag and drop is working again. It seems not to be a problem with different privileges in windows.
I have no clue where to look for this problem. Any advice is appreciated.
After some days of searching the web I could find the cause of the problem.
https://bugreports.qt-project.org/browse/qtbug-28601
In our software you can toggle the size of the module which uses a call to setWindowFlags. After that no more drag and drop events are processed.
I could workaround the problem by calling:
setAttribute( Qt::WA_AcceptDrops, false );
setAttribute( Qt::WA_AcceptDrops, true );
at the widgets which need the drag and drop. Hopefully we're updating to Qt 5.x soon. :/