One of the most common strategies to develop new software is to take advantage of existing source code, which is available in comprehensive packages called third-party libraries. As for all software systems, even these libraries change to offer new functionalities and fix bugs or security issues. The way the changes are propagated has been studied by researchers, interested in understanding their impact on the non-functional attributes of the systems source code. While the research community mainly focused on the change propagation phenomenon in the context of traditional applications, only little is known regarding the mobile context. In this paper, we aim at bridging this gap by conducting an empirical study on the evolution history of 291 mobile apps, by investigating (i) whether mobile developers actually update third-party libraries, (ii) which are the categories of libraries with respect to the developers' proneness to update their apps, (iii) what are the common patterns followed by developers when updating a software library, and (iv) whether high- and low-rated apps present peculiar update patterns. The results of the study showed that mobile developers rarely update their apps with respect to the used libraries, and when they do, they mainly tend to update the libraries related to the Graphical User Interface, with the aim of keeping the mobile apps updated with the latest design tendencies. In some cases developers ignore updates because of a poor awareness of the benefits, or a too high cost/benefit ratio. Finally, high- and low-rated apps present strong differences.