Email html code changed

Hi all,

I’m trying to configure custom emails for new users, and I have a little problem. I use a text editor (notepad++) to write the html code for emails, and then copy and paste the code into plugin emails page. But when I save the changes, for some reason, the HTML code were reformatted. For example, all the images referenced on this way:
src="http://mydomain.org/image.gif"
change to
src="//mydomain.org/image.gif"

someone knows why this occurs?

Thanks in advance!

https://wordpress.org/plugins/theme-my-login/