WPF Drag and Drop functionality vs. mark item text

See more:

C#

WPF

Hello,

i got a little problem here with my wpf ui.
There is a drag and drop functionality implemented using the PreviewMouseDown and PreviewMouseMove events on the source list box and the drop event at the target list box.
Now i got the problem, that it fires a System.InvalidOperationException with the message "Dispatcher processing has been suspended, but messages are still being processed.".
That occurs if the item is selected and the user moves the mouse with pressed left button to mark the text to edit it.

How do i know, that an item or the item, which is tried to drag, is in "edit mode" or something like that, so i can disable the drag in the PreviewMouseMove event (don't call DoDragDrop).

i mean something like that "listbox.Item.IsInEdit" so i can do something like this:
if ( ! lbXYZ.Item.IsInEdit)
{
...
DoDragDrop(...)
...
}

any suggestions?