Sitecore ECM says I must choose a Web page before editing message

I'm attempting to Create a One-Time One-Column message in Sitecore 7.5 ECM, but every time I do I am presented with the message:

You must choose a Web page before you may edit this message.

I can create one and manually select the webpage (Message Root) within Sitecore, but why doesn't it automatically select it in the ECM (SPEAK) interface?

It sounds like the relations are not being setup for the mail message when a message is created.

I haven't checked this process in later versions of ECM but this is what should happen:

1. When a message is created the item:created event is fired. The message gets created from a branch template (/sitecore/templates/Branches/Email Campaign/Messages/One-Column Message)

2. The RootItemEventHandler class calls a MessageRelationsCorrector class that corrects the relations of the mail message so that the datasources are correct for the mail message. E.g. the $name in the message will actually get replaced with the name of the new message you have created.

The example images below are the datasource values of one of the controls on the MessageRoot item and and the body field on the message item for the One Column Message Branch template.

In order for ECM to create the message correctly these values must be in place at /sitecore/templates/Branches/Email Campaign/Messages/One-Column Message

It is likely that some of these paths might have been changed or they are incorrect or the pipeline that corrects the messages is not running.