I have page with XhtmlString property in several languages (en, sv) without fallback. Also I created block in 'en' branch.

If I drag'n'drop this block to XhtmlString property in 'sv' page user will get error. There is no error in edit and preview context.

Stack Trace: 

[ArgumentNullException: Value cannot be null.
Parameter name: subject]
   EPiServer.Web.Mvc.Html.IContentDataExtensions.RenderContentData(HtmlHelper html, IContentData contentData, Boolean isContentInContentArea, String templateTag) +394
   EPiServer.Web.Mvc.Html.XhtmlStringExtensions.RenderFragment(IStringFragment fragment, HtmlHelper htmlHelper, UrlResolver urlResolver, IContentLoader contentLoader, TextWriter writer) +600
   EPiServer.Web.Mvc.Html.XhtmlStringExtensions.RenderXhtmlStringToWriter(HtmlHelper htmlHelper, XhtmlString xhtmlString, UrlResolver urlResolver, IContentLoader contentLoader, TextWriter writer) +306
   EPiServer.Web.Mvc.Html.XhtmlStringExtensions.RenderXhtmlString(HtmlHelper htmlHelper, XhtmlString xhtmlString) +48
   ASP.util_views_shared_displaytemplates_xhtmlstring_ascx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in D:\Workspace\Workflow\M2B\Sources\m2b-001\Sources\M2B.Site.WebUI\Util\Views\Shared\DisplayTemplates\XhtmlString.ascx:4
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +131
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +150
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +246
   System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer) +85
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +150
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5363

We are using EPiServer CMS 8.9