Have you first checked how it shows up in TwentyTen unmodified template? If it does work properly with TwentyTen, then you need to change someting in your own template.
Found this !isset bit today again even in Twentyten and TwentyEleven themes which I had never used. But my Contact 7 is clean.
And I got in on 2 sites which didn’t have Contact 7.
And my sites had the latest WP and all plugins updated.
So there must be various entrances.