Sometimes -- and I'm not sure exactly when or why -- I find that my slides pick up a vertical offset. Every slide except the first one is shifted downwards by a few pixels. This is frustrating if you have a background image that you would like to align exactly the same way on every slide. The fix, found here, turns out to be:
- use a newer version of PGF (I think 2.0 or greater), or
- insert the following in the preamble:
\makeatletter \let\Hy@FixNotFirstPage=\relax \makeatother
The issue apparently has something to do with a strange interaction between the hyperref and pgf packages.
