non-MH mail directories depend on files not changing inode number
    Messages are stored in non-MH mail directories with a name based
    on the inode number of the file containing the message.  If such a
    directory is copied to a different location or restored from tape,
    inode number may change, introducing the possibility of messages
    being overwritten.

SENDMAILFLAGS variable is treated as a single argument to sendmail
    The assignment SENDMAILFLAGS="-oi -odd" doesn't work as expected
    as procmail will pass it to sendmail as one argument.

TIMEOUT doesn't always work
    If a shell is invoked then procmail may wait while executing a
    command for longer than TIMEOUT specifies.

Variable capture actions overwrite before executing
    Variable capture actions clear the value of the variable being
    captured before the action is executed, thus causing the following
    action, for example, to not work as desired:
	variable=|echo "$variable" | tr '[A-Z]' '[a-z]'

regexp matching bug
    Some regexps may return an incorrect value in the MATCH variable,
    in particular when 'redundant' * or + operators appear on the left-
    hand side of the \/ token.