[exim] Why does this regex not match?

So I've got mail that has headers like this

From: "=?windows-1255?B?4+X46fog+ezp5S349Oz38eXs5eLp+g==?="
<info@???>

Subject:
=?windows-1255?B?7PHl6/j66e0g5ezu6+Dl4ekg+OLs6entIC0g7uXu7uz1IOHp5fr4?=

and so I have regular expressions like this

$header_from: does not match "\\s*=\\?(ks_c_5601-|big5|euc-|shift-jis|
(iso.\{0,4\}639-)|hkscs|sil|koi[78]|iscii|guobiao|gb2312|gb18030|(iso.\
{0,4\}2022)|(iso.\{0,4\}8859-[57])|(windows-1251)|(windows-1255))" and
$header_content-type: does not match "\\s*=\\?(ks_c_5601-|big5|euc-|
shift-jis|(iso.\{0,4\}639-)|hkscs|sil|koi[78]|iscii|guobiao|gb2312|
gb18030|(iso.\{0,4\}2022)|(iso.\{0,4\}8859-[57])|(windows-1251)|
(windows-1255))" and
$header_subject: does not match "\\s*=\\?(ks_c_5601-|big5|euc-|shift-
jis|(iso.\{0,4\}639-)|hkscs|sil|koi[78]|iscii|guobiao|gb2312|gb18030|
(iso.\{0,4\}2022)|(iso.\{0,4\}8859-[57])|(windows-1251)|(windows-1255))"

save $home/Maildir/.INBOX.intray.backup/

Now whilst this regular expression is quite convoluted even if I just
put $header_from: does not match "windows" it still doesn't match

Can anybody tell me why that's the case?

In my case I don't want to copy mail with foreign charsets etc into
the backup folder which is why copying it is conditional that it
doesn't match those patterns.