In this paper we present a case study about the clustering of maintenance activities applied on large software systems, from the complex networks perspective. We analyze several releases of two large Open Source Java software systems, using data extracted from Software Configuration Management systems and from Issue Tracking systems (ITS). We find that Java files affected by maintenance activity are likely to be connected with each other, forming interconnected clusters inside the software network associated to the software system. This means that Java files interested by the maintenance activities requested on ITS are likely to be connected each other through dependencies at the source code level. The information carried by the clusters of Java files may be used to improve strategies for large maintenance operations. Since the tendency to form clusters can vary across different systems, such analysis can also be a useful indicator of the impact of defects on source code files in different software systems.