BCC Batch Mode Destroys Email in Subsequent Batches

[eluser]Unknown[/eluser]
When using BCC Batch Mode the first batch of recipients get a good version of the email and the second batch of recipients get a messed up version. Here's example source from the emails:

Source from an email delivered to a recipient in the first batch (the way the email was intended to be delivered):

Code:

This is a multi-part message in MIME format.
Your email application may not support this format.

--B_ALT_4a8f2d8df2a68
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit

Here's a test message compiled in TinyMCE and sent in bcc batch mode using
CodeIgniter.To unsubscribe from future mailings please click here or follow
this
URL:http://www.[xxxxxxxxxxxxxxxx].com/index.php/group_mailer/unsubscribe


--B_ALT_4a8f2d8df2a68
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

&lt;html&gt;&lt;head>&lt;title&gt;&lt;/title>&lt;/head&gt;&lt;body><p>Here's a test message compiled i=
n TinyMCE and sent in bcc batch mode using CodeIgniter.</p><br /><br /><br =
/><p style=3D"color:#888; font-size:9px;">To unsubscribe from future mailin=
gs please <a >click here</a> or follow this URL:<br >http://www.[xxxxxxxx=
xxxxxxxx].com/index.php/group_mailer/unsubscribe</p>&lt;/body&gt;&lt;/html>

--B_ALT_4a8f2d8df2a68--

Source from an email delivered to a recipient in the second batch (here's where it gets messy)

Code:

This is a multi-part message in MIME format.
Your email application may not support this format.

--B_ALT_4a8f2d8e03df1
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit

Here's a test message compiled i=
n TinyMCE and sent in bcc batch mode using CodeIgniter.To unsubscribe from
future mailin=
gs please click here or follow this URL:http://www.[xxxxxxxx=
xxxxxxxx].com/index.php/group_mailer/unsubscribe


--B_ALT_4a8f2d8e03df1
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

&lt;html&gt;&lt;head>&lt;title&gt;&lt;/title>&lt;/head&gt;&lt;body><p>Here's a test message compiled i=
=3D
n TinyMCE and sent in bcc batch mode using CodeIgniter.</p><br /><br /><br =
=3D
/><p style=3D3D"color:#888; font-size:9px;">To unsubscribe from future mail=
in=3D
gs please <a >click here</a> or follow this URL:<br >http://www.[xxxxxxxx=
=3D
xxxxxxxx].com/index.php/group_mailer/unsubscribe</p>&lt;/body&gt;&lt;/html>

--B_ALT_4a8f2d8e03df1--

It almost looks like the second batch goes through a prep function twice instead of once. Anyone have any ideas on how to fix this? I'm using CI 1.7.1.

Also - this is what happens to the subject (it gets removed):

Code:

Subject: =?ISO-8859-1?Q?Test_Subject?=

Turns into:

Code:

Subject: