3.9 Beta 1 – gallery preview in editor not working with small images

Hi All,

The gallery preview doesn’t work in the content editor when the gallery contains an image smaller than 150 pixels in width and height, I get the following error in the console:
TypeError: attachment.sizes.thumbnail is undefined
in the underscore.min.js file.
I can see that the shortcode is added in the Text tab, however the Visual tab preview is not working.

I have experienced this problem with different themes, including the default WordPress themes.