o "_" is not escaped, and causes TeX to abort, thinking it's a
  subscript outside of maths mode.  Most of my table and field names
  use underscores, so this is a really nasty one.
o The column count is calculated using the contents of opt_align. But
  opt_align has one extra element, and so it's always one too many.  I
  changed it to count the column headings, like all the other output
  formats.  There may be a bug in computing opt_align that this patch
  does not address, but I'm not yet familiar enough with the psql
  source to fix this as well.
o  The line drawing rules for each border setting (0-3) and expanded
  mode didn't always match the documented behaviour and what other
  formats (e.g. aligned) did.  I made it as conformant as possible,
  and also tidied the alignment of the first line of the footer, which
  was incorrectly indented.

Roger Leigh