This post on the forum describes your issue, however it's related to iphone. My answer was to check the image quality setting of the widget, and see if that has impact. Anyways here it's working fine on mx6 and ios/android devices.
Can you let us know what the image quality settings are, and if changing this to i.e. 500 solves your issue?
The image quality was set to 150x150 and the appearance as well.
I increased the image quality to 500x500 and then I was able to save the picture in my Xiaomi, which I was not able to before.
I also increased the appearance to 500x500 and 250x250 and I was also able to see the preview image in both cases, which I was not able to before in neither of the android phones.
I guess it's a resolution issue, it seems it can't go lower than a certain size.
Thank you very much!! Never thought it could be an image quality issue.