Here is an excerpt from my muttprint configuration:

REM_QUOTE="off"
REM_SIG="off"
SIG_REGEXP="^-- $"
VERBATIMNORMAL="numbers=left,stepnumber=5"
VERBATIMSIG="fontshape=it,frame=topline"

muttprint is called by mutt with no arguments. Whatever the SIG_REGEXP
configuration, muttprint ignores the signatures of the mails it parses. I know
about the space in the delimiter, and I've tested this with more than one
message.

This problem is not quite the same as #280083, however the version sent by
Bernhard Walle in this report fixes it.