UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3013.3 Safari/537.36

Example URL:

Steps to reproduce the problem:
1. Make sure check the "Ask where to save each file before downloading" in settings.
2. Click an click-to-download link for an mp4 video file.
3. 

What is the expected behavior?
An window pop out prompting for location. And after I chose the location I want and click save. Then the downloading starts. When downloading finishes, the file is not opened unless I click it.

What went wrong?
The downloading starts without asking for location(it downloads to default location) and when the downloading finishes, the file is opened by the system default player.

Did this work before? N/A 

Chrome version: 58.0.3013.3  Channel: dev
OS Version: OS X 10.9.5
Flash Version: Shockwave Flash 25.0 r0

Only mp4 file acts like this, any other type files even video files(flv, mkv,..etc) are still normal.

I can still download some mp4 file to where I want by "rightclick->save link as" or playing a mp4 in chrome and "rightclick->save Video as". But when the downloading finishes, the mp4 files are still opened automatically.