UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.87 Safari/537.36

Steps to reproduce the problem:
Internal plugin PDF-Viewer, 
in version 48, the save button has a image like a floppy disk,
in version 49, the save button has been replace by download and the image is like an arrow pointing down

My web application generate a PDF and open a html pop-up as a content type application/pdf to display it. But once the PDF is out at the client with the internal plugin PDF-viewer, and this work correctly, the PDF file on the server is deleted.

At this point everything is OK and the client still has the popup open with the PDF displayed.

The problem start when you try to Save/Download the PDF.
Sometimes the PDF is save correctly, something the download button try to request the server with the same URL before saving the document, but the file doesn't exists anymore on the server, causing the save to not work

How to reproduce it?
This will still work.... let me explain  :)
Open a PDF file directly from an URL like, that www.server.com/file.pdf, then rename the file on the server while its open at the client, then try save the PDF.
I'm not able to reproduce the problem like this.

This will "sometimes" cause this issue. 
Can be hard to reproduce. On my computer I'm not able to reproduce the issue, but alot of users in my company have this issue, and I saw it and work around with it to really see what is going on.
Open a PDF from a web application in a popup like that www.server.com/openfile.php, as a content-type application/pdf, then once open, delete the file on the server, then try to save the PDF.
This is where the problem can sometimes occur.
If you still save a PDF, close the popup and start again the process, and after some tries, It will not be able to save the PDF.
In my case what I saw is, when clicking on download, it does a request with the same URL at the sever before saving the PDF file. and this is not suppose to happend...

What is the expected behavior?
when saving a PDF to not request the server again, save what is downloaded at the client

What went wrong?
sometimes the download PDF request the server before saving

Did this work before? Yes version 48 and earlier

Chrome version: 49.0.2623.87  Channel: stable
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: Shockwave Flash 21.0 r0

We are using Chrome with our Web app on the same computers all over the company and the application has not change, for the past 2 years, suddenly, it start to happen monday morning, march 14 2016, I saw some browser to version 48, that has the version 49 pending, the restart was needed, then the problem start to happen