R – Is it possible to put a Content Editor Web Part in a sharepoint app page

You can use the SPLimitedWebPartManager class to manipulate Web parts on a Web part page. An instance of this class can be obtained from an SPFile object as follows:

using (SPSite site = new SPSite("<site url>"))  // e.g. http://server/sites/asite
using (SPWeb web = site.OpenWeb())
{
    SPFile file = web.GetFile("<page url>");   // e.g. /sites/asite/default.aspx
    SPLimitedWebPartManager lwpm = file.GetLimitedWebPartManager();
    SPLimitedWebPartCollection webParts = lwpm.WebParts;
    WebPart wp = webParts[<id, index or Guid>];

    // Add your code to update the Web Part

    lwpm.SaveChanges(wp);
}

You can also add or delete web parts with the SPLimitedWebPartManager.

Have you changed anything about the layout recently? It seems a bit like the issue described here: http://blog.mastykarz.nl/css-causes-javascript-error-while-moving-web-parts-in-edit-mode/ (except for the Web Part getting blank).