[Exim] exim 3.34 - systemfilter and embedded newline chars

I recently upgraded from version 3.22 to 3.34 and now find that when the
systemfilter outputs newline characters as part of 'fail' text, they are
not converted to actual newline characters in the message.

For example :

the systemfilter contains - if <condition> then fail text "Message
failed\n\n$message_headers\n" endif

and what I get in the message is a block of text with '\n' where the
newlines should be. These also appear in the text included through
$message_headers.

Switching back to 3.22 solves the problem.

--Terry