Theme not falling back

Question

I have a website and I want to have my custom theme based on a previously installed theme which is a third party theme.
Previously installed theme is ABC.( set under Theme -> Default)
Now I have created my custom theme based on
http://devdocs.magento.com/guides/m1x/ce19-ee114/RWD_dev-guide.html
http://alanstorm.com/magento_parent_child_themes
But the theme is not falling back to ABC and trying to find files in my custom theme and if it is not able to find the file in custom theme it is giving 404 error for that file.
app/design/frontend/rwd/custom/etc/theme.xml

<?xml version="1.0"?>
<theme>
    <parent>rwd/ABC</parent>
</theme>

Directory path for parent theme :
app/design/frontend/rwd/ABC

skin/frontend/rwd/ABC

My custom theme skin directory :

skin/frontend/rwd/custom

Please help me to fix this issue.

Answer 1

I found the issue.
Issues are due to wrong coding standards were used.
There are many things in code which are hardcoded and prevented theme fallback functionality to happen.

Answer 2

In app/design/frontend/mycustomtheme/default/etc/theme.xml you need something like

<?xml version="1.0"?>
<theme>
<parent>default/ABC</parent>
<layout>
    <updates>
    </updates>
</layout>
</theme>

Then copy/create your layout and template changes in

app/design/frontend/mycustomtheme/default/layout app/design/frontend/mycustomtheme/default/template

If it still doesn't work, install the Alan Storm demo and modify this to point to your Parent theme.