UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2931.0 Safari/537.36

Steps to reproduce the problem:
1. Listen to dragenter on drop area
2. Drag XLS file onto drop area  

What is the expected behavior?
Expect kind of: "application/vnd.ms-excel"

What went wrong?
But found kind of ""

Did this work before? N/A 

Chrome version: 57.0.2931.0  Channel: canary
OS Version: OS X 10.12.1
Flash Version: