Kmail Spam/ham toolbar buttons disappear

I used the anti-spam wizard to install spam-assassin as a spam filter in kmail. The spam/ham buttons do not appear on the toolbar. However, when I open the configure toolbar dialog it shows them as installed on the toolbar - in the right panel at the end of the list of tools that really do show up. I’ve tried to move them up and down, remove them and then replace them on the toolbar, but it makes no difference.

How do I get them to actually show up on the toolbar? I’m using Kmail 1.12.4 on KDE 4.3.5