Hi Mike,
Its a bug, but its easily fixed. If you edit the file /Blog/EditPost.aspx with a text editor, look for this:
<asp:TextBox id="txtTitle" runat="server" Columns="50" maxlength="100" CssClass="forminput widetextbox"></asp:TextBox>
and change the maxlength to 255. The field in the db allows 255 chars. I am fixing this now in my copy so it will be fixed in the next release.
Hope it helps,
Joe