Chrome Version: 51.0.2704.106 (Official Build) (64-bit)
              also seen in 54.9.2797.0 (Developer Build) (64-bit)
Chrome OS Version: 8172.62.0 (Official Build) stable-channel link
                   
Chrome OS Platform: 

<b>Network info: <network, encryption type, router model (if known)></b>

Please specify Cr-* of the system to which this bug/feature applies (add
the label below).

Steps To Reproduce:
(1) Open Files app.
(2) Insert a USB drive with DCIM folder.
(3) Choose one of the image files in DCIM folder.
(4) Unselect all the files and click the Cloud Backup button.
(5) Make sure it says "All backed up to Google Drive!" (otherwise, wait until the backup finishes and go back to #4)
(6) Select one or more files. This can be either by giving keyboard focus on a file (click filename) or clicking icons.
(7) Click the down arrow (triangle) of the Cloud Backup button to expand the pulldown box.
Additionally,
(8) Click [BACK UP] button in the pulldown.

Expected Result:
The pull down box says something like:
"All these files are backed up to Google Drive."
Backup button should not appear there or should be disabled.

Actual Result:
It says the chosen files are new photos.
It also shows a button to trigger backup.
"%d new photo(s) found
 Ready to backup to Google Drive
                    [BACK UP]"

How frequently does this problem reproduce?
Always

What is the impact to the user, and is there a workaround? If so, what is
it?

By step 8, the files are copied again to Drive, producing multiple copies of the file like
"IMG_20160708123456.jpg"
"IMG_20160708123456 (1).jpg"
"IMG_20160708123456 (2).jpg"
"IMG_20160708123456 (3).jpg"
on the Drive, if the user repeats the operation.

Also, Steps 7 and 8 can be replaced by this single click.
(7') Click the Cloud Backup button (click left half of it; not expanding the menu by downarrow)
In this case, the system starts to backup the files and silently finishes it.