I hope you find this bug report more helpful that my previous.
On a fresh installation of MiKTeX 2.8, I used dvipng to generate png from two dvi files. The file relativity-11pt.dvi uses an 11pt font, while relativity-12pt.dvi uses a 12pt font.
[Install MiKTeX 2.8]
dvipng relativity-11pt.dvi 2> stderr-11pt-1.txt
dvipng relativity-11pt.dvi 2> stderr-11pt-2.txt
dvipng relativity-12pt.dvi 2> stderr-12pt-1.txt
dvipng relativity-12pt.dvi 2> stderr-12pt-2.txt
I expected the resulting .png files to match the contents of the .dvis.
For each dvi, the first run of dvipng resulted in several characters missing from the .png. All subsequent runs rendered correctly.
Note: This behavior occurs sporadically, presumably whenever a new font is used.
Original dvi, the resulting png, and logs