Cannot edit my own template

Hi all,
I have created my own template as described in the documentation. I am able to save it but when I try to load my template again, the code fields either stay empty or I see the HTML/CSS of the template I looked at before.

Here is what I do:
– Create new template & enter template name
– Save
– Select another template
– Select again my own template (fails)

A similar issue was described before but that was related to WAMP configuration. I use WP on a live server.

Do you have any idea what to do?

Thanks!