(In reply to Oliver Kellogg from comment #2)

> [...]
> However, the backtrace tells a different story:
> Somehow Umbrello thinks you are _moving_ the diagram in the list view, not
> double clicking on it.

Here is the fix for the crash in this case:

umbrello/clipboard/umlclipboard.cpp
- In function checkItemForCopyType() case Model_Utils::typeIsDiagram(type),
  check return value from doc->findView(item->ID()) against NULL prior to
  insertion into m_ViewList.

BUG: 338983