While doing a visual comparison of two pdf files, say,
http://www.debian.org/releases/stable/amd64/install.pdf.en
against itself (after copying under a different name),
the following message is output on the console from which diffpdf is
started:

Bogus memory allocation size

This message appears in lots of copies. I expect that if it is a
real-error message, it should be informative. If it not an error
message, diffpdf should not produce garbage on the console.

The impact of this message on the shown comparison result (same / not
same) is unclear.

Jaakov