Magento introduced the base/default theme in CE 1.4 and made this an absolute fallback (independent of configuration). Prior to this the "main" distribution theme was default/default. Developing third-party modules was a big mess before 1.4 because you couldn't know how the user's themes were configured. Since this time one always puts "new" assets in base/default.
However, Magento (for some reason, perhaps due to internal testing tools) never moved the adminhtml theme from default/default which stinks because it means you always have to specify a custom theme for adminhtml in case of changes. This issue is even further complicated by the core distribution of a third-party module with custom theme elements requiring Magento to ship with a custom theme already specified:
<default>ultimo</default><!-- or "anna" or whatever -->
Thankfully this module was removed from core distribution after 1.6.
For your 1.9 install, assuming it does not have a legacy
Find_Feed module, you have a few options in general. For you specifically though you need to see if Ultimo theme is making customizations to the Magento admin theme settings using one of these methods:
- You can move the entire adminhtml theme from default/default to base/default (I've tested, it works without a hitch), and then you can place customized files in default/default as they will be picked up without additional configuration. However, this is risky as an upgrade will replace the files under default/default. So, probably don't do this.
You can specify a custom theme via configuration...
(Note that this will add a fallback level above default/default, i.e. the system will resolve theme paths first under default/ultimo and then under default/default.)
...or via the new
theme.xml file, amply explained by Alan Storm.
You could also combine 1 & 2. and specify a new package (this would be my approach if the Ultimo theme has customizations and is not setting adminhtml theme or package in some crazy way.