Individual differences of developers in performance and introduced defects have been reported by many research studies and are frequently observed in software development practice. Thus, when the source of defects in the final product is discussed, developers are usually the first under suspicion. However, defects residing in a released software product are the result of defects introduced throughout the sequence of development activities (e.g., specification, design, implementation, testing and stabilization) less the defects detected and removed in these activities. This case study explores and describes the difference between developers in terms of associated post-release (i.e., delivered) defects. The results are put in relation to the intensity with which a developer’s changes and enhancements have been tested to identify a latent influence by pre-release quality assurance measures.