Wow, thanks for the quick response. I didn't know about the Network Log. That's a handy feature. Looking at the response I got from posting a new message I would say that it is definitely a Drupal issue.
Network message sent: 2008-01-20 16:00:01 -0900
URL: http://www.[domain].com/xmlrpc.php
Method name: metaWeblog.newPost
Network reply received: 2008-01-20 16:00:01 -0900
URL: http://www.[domain].com/xmlrpc.php
Method name: metaWeblog.newPost
Status code: 200
Succeeded: YES
Request text:
<?xml version="1.0" encoding="utf-8"?>
<methodCall>
<methodName>metaWeblog.newPost</methodName>
<params>
<param>
<value><string>1</string></value>
</param>
<param>
<value><string>[user]</string></value>
</param>
<param>
<value><string>[password]</string></value>
</param>
<param>
<value>
<struct>
<member>
<name>mt_allow_comments</name>
<value><int>1</int></value>
</member>
<member>
<name>mt_keywords</name>
<value><string></string></value>
</member>
<member>
<name>mt_convert_breaks</name>
<value><string>0</string></value>
</member>
<member>
<name>title</name>
<value><string>Test Post</string></value>
</member>
<member>
<name>mt_excerpt</name>
<value><string></string></value>
</member>
<member>
<name>description</name>
<value><string><p>Test post to Drupal 6 RC2 with MarsEdit...</p></string></value>
</member>
<member>
<name>mt_text_more</name>
<value><string></string></value>
</member>
<member>
<name>mt_allow_pings</name>
<value><string>0</string></value>
</member>
</struct>
</value>
</param>
<param>
<value><boolean>0</boolean></value>
</param>
</params>
</methodCall>
Response text:
<?xml version="1.0"?>
<methodResponse>
<params>
<param>
<value><string>10</string></value>
</param>
</params>
</methodResponse>
Network message sent: 2008-01-20 16:00:01 -0900
URL: http://www.[domain].com/xmlrpc.php
Method name: metaWeblog.editPost
Network reply received: 2008-01-20 16:00:02 -0900
URL: http://www.[domain].com/xmlrpc.php
Method name: metaWeblog.editPost
Status code: 200
Succeeded: YES
Request text:
<?xml version="1.0" encoding="utf-8"?>
<methodCall>
<methodName>metaWeblog.editPost</methodName>
<params>
<param>
<value><string>10</string></value>
</param>
<param>
<value><string>[user]</string></value>
</param>
<param>
<value><string>[password]</string></value>
</param>
<param>
<value>
<struct>
<member>
<name>mt_allow_comments</name>
<value><int>1</int></value>
</member>
<member>
<name>mt_keywords</name>
<value><string></string></value>
</member>
<member>
<name>mt_convert_breaks</name>
<value><string>0</string></value>
</member>
<member>
<name>title</name>
<value><string>Test Post</string></value>
</member>
<member>
<name>mt_excerpt</name>
<value><string></string></value>
</member>
<member>
<name>description</name>
<value><string><p>Test post to Drupal 6 RC2 with MarsEdit...</p></string></value>
</member>
<member>
<name>mt_text_more</name>
<value><string></string></value>
</member>
<member>
<name>mt_allow_pings</name>
<value><string>0</string></value>
</member>
</struct>
</value>
</param>
<param>
<value><boolean>1</boolean></value>
</param>
</params>
</methodCall>
Response text:
<?xml version="1.0"?>
<methodResponse>
<params>
<param>
<value><boolean>1</boolean></value>
</param>
</params>
</methodResponse>
Network message sent: 2008-01-20 16:00:03 -0900
URL: http://www.[domain].com/xmlrpc.php
Method name: metaWeblog.getPost
Network reply received: 2008-01-20 16:00:03 -0900
URL: http://www.[domain].com/xmlrpc.php
Method name: metaWeblog.getPost
Status code: 200
Succeeded: YES
Request text:
<?xml version="1.0" encoding="utf-8"?>
<methodCall>
<methodName>metaWeblog.getPost</methodName>
<params>
<param>
<value><string>10</string></value>
</param>
<param>
<value><string>[user]</string></value>
</param>
<param>
<value><string>[password]</string></value>
</param>
</params>
</methodCall>
Response text:
<?xml version="1.0"?>
<methodResponse>
<params>
<param>
<value><struct>
<member><name>userid</name><value><string>[user]</string></value></member>
<member><name>dateCreated</name><value><dateTime.iso8601>20080120T20:00:01</dateTime.iso8601></value></member>
<member><name>title</name><value><string>Test Post</string></value></member>
<member><name>postid</name><value><string>10</string></value></member>
<member><name>link</name><value><string>http://www.[domain].com/node/10</string></value></member>
<member><name>permaLink</name><value><string>http://www.[domain].com/node/10</string></value></member>
<member><name>content</name><value><string><title>Test Post</title></string></value></member>
<member><name>description</name><value><string></string></value></member>
<member><name>mt_allow_comments</name><value><int>1</int></value></member>
<member><name>mt_convert_breaks</name><value><string>0</string></value></member>
</struct></value>
</param>
</params>
</methodResponse>
Network message sent: 2008-01-20 16:00:03 -0900
URL: http://www.[domain].com/xmlrpc.php
Method name: mt.getPostCategories
Network reply received: 2008-01-20 16:00:04 -0900
URL: http://www.[domain].com/xmlrpc.php
Method name: mt.getPostCategories
Status code: 200
Succeeded: YES
Request text:
<?xml version="1.0" encoding="utf-8"?>
<methodCall>
<methodName>mt.getPostCategories</methodName>
<params>
<param>
<value><string>10</string></value>
</param>
<param>
<value><string>[user]</string></value>
</param>
<param>
<value><string>[password]</string></value>
</param>
</params>
</methodCall>
Response text:
<?xml version="1.0"?>
<methodResponse>
<params>
<param>
<value><array><data>
</data></array></value>
</param>
</params>
</methodResponse>