Plain text attachments are not identified as Attachment parts

[Denitz]

Receiving email from gmail with plain text attachment file, here are the part details:

stdClass Object
(
    [type] => 0
    [encoding] => 3
    [ifsubtype] => 1
    [subtype] => PLAIN
    [ifdescription] => 0
    [ifid] => 0
    [lines] => 434
    [bytes] => 21690
    [ifdisposition] => 1
    [disposition] => ATTACHMENT
    [ifdparameters] => 1
    [dparameters] => Array
        (
            [0] => stdClass Object
                (
                    [attribute] => FILENAME
                    [value] => filename.txt
                )

        )

    [ifparameters] => 0
    [parameters] => stdClass Object
        (
        )

)

AbstractPart::isAttachment() does not detect it as attachment because subtype is 'PLAIN':

self::SUBTYPE_PLAIN !== \strtoupper($part->subtype)

[Denitz]

Still a problem on current 1.5.4, any news?

[Slamdunk]

Bugfix released in 1.5.5