This question concerns the native /_ui/core/email/author/EmailAuthor system.
I can pass values to the form in the URL like so:
p2_lkid = To field
p3_lkid = Related to field
template_id = ID of template to use
If I select a template manually using the Select Template button on the form then the body of the email (and the template) will be editable inline.
However if I load a template automatically by passing its ID as a parameter to EmailAuthor then whilst the template will load into the body it will become read only.
How can I make the template load automatically into the body whilst retaining the feature to modify edit inline?