Recent studies have shown Multiple Network Interfaces (MNI) offer inexpensive solutions toward improving the reliability of communication over multiple paths, balancing load among paths, and enhancing quality of service by aggregating bandwidth. Especially, recent studies on emerging multipath transport protocols have shown that they perform concurrent multipath transport and bandwidth aggregation quite well when packet drop rates and bandwidths of the paths are not far apart. However, in shared networks these parameters for all paths cannot be expected to be close throughout the lifetime of the connection. For instance, packet drop rates and available bandwidths are known to vary dynamically in wireless links, which have been deployed extensively. However, to the best of our knowledge no study has been reported for path imbalances involving multiple parameters. In this paper we propose a software architecture that captures high level design of two concurrent multipath transport protocols. These two protocols have been implemented on the same computing and networking environments for a meaningful evaluation under path imbalances. In our network emulation laboratory, two host computers were connected through two independent network emulators. Each network emulator runs on a separate computer, and the network parameters are adjusted independently. Our extensive experimentation with these protocols show that imbalances of path parameters drastically degrade the performance under certain conditions while an imbalance may have less impact on other conditions. The study also reveals a counter intuitive fact that even an increase in packet drop rate along a path may marginally improve rather than deteriorate the overall throughput under certain conditions. The performance of one of the protocols was found to be robust against variations of packet drop rate and bandwidth across paths.