Incompatibility between applications developed on top of frameworks with new versions of the frameworks is a big nightmare to both developers and users of the applications. Understanding the factors that cause incompatibilities is a step to solving them. One such direction is to analyze and identify parts of the reusable code of the framework that are prone to change. In this study we carried out an empirical investigation on 11 Eclipse SDK releases (1.0 to 3.7) and 288 Eclipse third-party plug-ins (ETPs) with two main goals: First, to determine the relationship between the age of Eclipse non-APIs (internal implementations) used by an ETP and the compatibility of the ETP. We found that third-party plug-in that use only old non-APIs have a h...