So I am implementing Episerver forms for a customer. Their PreviewBlockController looks like so:

[TemplateDescriptor(
        Inherited = true,
		Tags = new string[] { RenderingTags.Preview },
		TemplateTypeCategory = TemplateTypeCategories.MvcController)]
	public class PreviewBlockController : ActionControllerBase, IRenderTemplate
    {
		public ActionResult Index(IContent currentBlock)
		{
            const string masterLayoutFull = "_BlockEditLayout";

			// Setup edit mode for any block
			ViewBag.BlockInEditMode = EPiServer.Web.Routing.Segments.RequestSegmentContext.CurrentContextMode == ContextMode.Edit;

			var baseType = currentBlock.GetType().BaseType;

		    if (baseType == typeof (TeaserBlock))
		        return View("~/Views/Blocks/TeaserBlock/Edit.cshtml", masterLayoutFull, new TeaserBlockViewModel(currentBlock as TeaserBlock));

Naturally Ill insert something like

if (baseType == typeof(FormContainerBlock))
		    {
                return View("~/Views/Shared/ElementBlocks/FormContainerBlock.ascx", currentBlock as FormContainerBlock);
		    }

The problem is that currentBlock.Form == null which makes the form render with the message

"<%--in case formcontainerblock is used as a property, we cannot build form model so we show a warning message to notify user--%>" (its from this bug, not applicable to my case I think: LINK)

The forms renders well (Form prop is populated) when its rendered in a contentarea on a page, both on the site and in edit mode (on the page).

Anyone have any idea of whats up here?

(I tried creating a new preview controller inheriting from FormContainerBlockController as seem to work here LINK but with the same error, I also tried using fetching the block from the database with Icontentloader with the same effect)