The grid module would have to add some decode HTML functionality. I would think that content pulled from the text/html module would result in the same problem. All content captured by the forum module goes through the core security filters. You can see this in the PostToDataBase() method at: If you look in Components\UI\Posts.vb you will see this content is decoded within the RenderPostBody method via:

Body = objSecurity.InputFilter(_Body, PortalSecurity.FilterFlag.NoScripting)

Dim bodyForumText As ForumText = New ForumText(System.Web.HttpUtility.HtmlDecode(Post.Body), ForumConfig)