Yes the problem exists:
Template="Exit,Save,ChangeParagraph,Seperator,.... -> OK
Template="Exit,Save,Seperator,ChangeParagraph,... -> Display another Seperator instead of ChangeParagraph
System.Web.UI.WebControls.Image Image2 = new System.Web.UI.WebControls.Image ();
Image2.ID = "ChangeParagraph";
Image2.ToolTip = "Change Paragraph";
Image2.ImageUrl = "/images/paragraph.gif";
Image2.CssClass = "button";
Image2.Attributes.Add("onclick","alert('Hi');");
Image2.Attributes.Add("type","btn");
Editor1.RegisterCustomButton(Image2);