As of ADT 14, resource constants in library projects are no longer final. This is explained in greater detail in this document.
However, one consequence of this is that some existing projects no longer compile when you use ADT 14. And the reason may be hard to understand. To help with this, there's a new quickfix detector which looks for a specific compiler error and when present adds a "quickfix". This means that when you hover over the error it offers more help:
If you select this quickfix you get this dialog:
Hopefully this will make it much more obvious what's going on, and make it a lot less painful to update any code which depended on constants in library project resources.