Cannot drag and drop while file operation in progress

* Start a long file operation such that the progress window appears.
* Try to carry out an unrelated drag and drop operation - it fails to start. However the equivalent operation using copy/paste works OK.

---
Want to back this issue? **[Post a bounty on it!](https://www.bountysource.com/issues/75537436-cannot-drag-and-drop-while-file-operation-in-progress?utm_campaign=plugin&utm_content=tracker%2F65602118&utm_medium=issues&utm_source=github)** We accept bounties via [Bountysource](https://www.bountysource.com/?utm_campaign=plugin&utm_content=tracker%2F65602118&utm_medium=issues&utm_source=github).