About SharePoint:FormField and custom column

Yesterday, i had to face SharePoint again.
I created a custom type note field in which i inject custom HTML code (generated by code behind):

and a custom edit form (for the related custom content type) in which i want to show this field.

When i run the form, i noticed the field was blank...
What i've done to solve the problem?
This was driving me mad, i solved just setting the No value to the Append Changed to Existing Text option of the custom field.

The wanted

Voilà, smooth and clean!