If you create a new HTML template in a personal theme, this template is multiplied in all the themes you have installed. I think this is a bug and a solution should be found.

Please developers IPS to review this.

Can you clarify why this would be a bug?

Imagine you have 2 themes and you use the template on a page or in a custom app.. what should happen in the theme where your custom template isn’t available ? 

46 minutes ago, Daniel F said:

Can you clarify why this would be a bug?

Imagine you have 2 themes and you use the template on a page or in a custom app.. what should happen in the theme where your custom template isn’t available ? 

When editing a theme and using a new template, this template should only affect the theme in which it was created.
What logic has a change in one theme to multiply in all themes?

... If you're tuning one of your cars, this tuning is only for this car, not for your other car. Your two cars create a different feeling for you, but you are - with your different idea of every moment of your life.
This is also a site - in one theme you express an idea, another theme - another idea. You can change the themes default of your choice.

Without logic, if you type a new template into one of your themes, this template will automatically edit all your themes by adding to it.