Every profile type has key metrics measures that are specific for the profile type. Facebook profiles will include measures like "Likes", Twitter profiles will have "Tweets", and a standard web profile will have "Page Views".
When you create a REST URL for key metrics in the REST URL Generator, and you select the method "Get key metrics for the default profiles in all spaces", all the measures necessary for all the space types will be automatically provided.
This means if new space types have been added to an account, and the user has previously generated a REST URL that used the "Get key metrics for default profiles of all spaces" method in Generator, there will be a change in the measures displayed. This can mean the destination application may need to be reconfigured to account for the new columns that appear in the data.
A work around is to use only the "Get key metrics for a specific profile" method and produce a separate REST URL for each profile. This will prevent undesired measures from appearing in the REST data.