Duplicated sketches no longer save after an image upload

[aiboyles]

Nature of issue

• Found a bug

Details about the bug:

• Steps to reproduce this bug:

1. Take an existing sketch and duplicate it.
2. Upload a file, such as an image. (Either from the left hand side menu, or the Sketch > Add File option from the menu).
3. Try to save the sketch (File > Save).

The sketch will not save. An pop up message box often appears that says:
"Error: The project you have attempted to save has been saved from another window. Please refresh the page to see the latest version."

I noticed this issue starting to occur a couple of weeks ago, perhaps around April 8th.

[catarak]

Thanks for reporting! This is a bug caused by a recent pull request, #1039.