The Summer '13 release for Salesforce.com included an awesome feature that many developers were clamoring for. When refreshing a sandbox, the platform (pre-Summer 13) simply copied the metadata for custom settings. With Summer '13 you also got the data!
I just refreshed one of our sandboxes and indeed the custom settings data copied successfully. I could query the custom object for a specific setting and it was definitely there. However, when I ran all of my unit tests a number of them failed. Upon further investigation I discovered that the following returned
Platform_Settings__c p = Platform_Settings__c.getInstance('SOME-NAME');
Strange because the data was definitely there. I ran the following and all of my settings indeed came back.
So in the end I had to copy the values from my existing custom setting and into a new one. Only then were my test cases able to run successfully. Has anyone else seen this issue?