I upgrade to X5 v12, imported my website, all looks great. I worked on page responsive setting, again all works fine. Then I worked on the Header responsive template. I did not touch the main template header. I opened the Responsive Template Structure, went to the header and picked a generic image. Did a preview and all looks fine, desktop size shows the regular main header, smaller sizes change to the graphic added under responsive template header. All OK. Go back into the designer and look at the Main Template Structure and the main header is gone (blank). The preview image of the website in the designer (when you pick your web site shows it missing too). Preview and it is missing too.

I've duplicted the working web site three times and tired to add a responsive template header image and each time it has deleted the image of the main template header. The responsive template image is still there and works.

(as a side note, when you utilize a template and you have the default template header image top.jpg - is there a way to put it back?)