The source-code integration process is critical for any distributed, large-scale open-source software (OSS) project. It serves as an implicit or explicit quality control gate and is inherently of a socio-technical nature in that the bare technical act of merging new code contributions is preceded by (oftentimes engaged) discussions and reviews. Given the reasonable and widely accepted assumption that professional experience and seniority lead to higher social credit in communities, more experienced developers are expected to get favored in this process, manifesting in higher probabilities of receiving feedback on contributions, or getting contributions accepted. We conjecture that exceptions to this pattern may indicate procedural issues and examine this hypothesis through a mixed-method study. To this end, we use developer coreness, a continuous proxy measure of experience that measures how important and connected a developer is within a project. We then study code integration processes of 16 popular OSS projects, employing a new methodology to measure the impact of developer coreness on these processes. This allows us to identify process-deviant projects, which we investigate qualitatively to determine whether unexpected observations indicate underlying procedural issues. A key insight of our study is that the conjecture that developers with higher coreness have a higher probability to receive feedback and to have their patches accepted usually only holds for projects where the community follows a systematic process of sending all new patches to the mailing list for review. In projects where (some) developers are less strict when keeping up with the submission guidelines, our results are less consistent and less pronounced. We even find that in these situations there are possible procedural problems that can lead to quality issues with the software. This shows that our methodology can be used to find indications of procedural problems in OSS projects, which is a prerequisite for solving these problems. By means of semi-structured expert interviews, we confirm that the project communities are interested in such findings and are actively working on fixing procedural problems in the integration process.