Just a work around i found, it doesn't fix the problem, but i think it can help to find it.
In the dynamic_forms.php file i commented this lines
case "ALT_TEXT":
return true;
to be able to remove the field, then i removed it, and created a new html editor field, edited the template to remove the old one and add the new one, and it is working as expected.
Even tho, there are some issues, since the ALT_TEXT is missing:
I'm getting message "Configuration error: Failed to bind the "ALT_TEXT" Template Tag. (not defined)" in the publisher interface after i edit something.
And in the "your pixels" grid in the publisher interface i have the "date" "link" "pixels" "expires" "status" rows, but not the text row.
So i think that the problem is not in the editor, but its a problem with this field name in particular, unfortunally i tried to read the script but im not a coder and its too long, so couldn't fix it.