When I post a form with Button.PostBackUrl set to an other page than current I get the following error:

[HttpException (0x80004005): The file '/' does not exist.]
   System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) +12678292
   System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) +203
   System.Web.Compilation.BuildManager.GetVPathBuildResult(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean ensureIsUpToDate) +192
   System.Web.UI.Page.get_PreviousPage() +149
   EPiServer.Web.PageExtensions.ServerTransferBugfix.page_PreRenderComplete(Object sender, EventArgs e) +44
   System.EventHandler.Invoke(Object sender, EventArgs e) +0
   EPiServer.PageBase.OnPreRenderComplete(EventArgs e) +19
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4628

In the above case I post from start page to "/other-page". The Alloy site renders the same result.