The proliferation of smartphones and related high-bandwidth services such as video streaming or cloud services are leading to increasing traffic demands, hence to the need of more efficient mobile networks. As current 4G networks are nearing their capacity, there is growing interest for the inclusion of new spectrum bands for LTE networks, among which unlicensed spectrum features prominently. Coexistence issues are all but certain, especially in the 5 GHz unlicensed band, where incumbent, ubiquitous WiFi devices are likely to be affected. Many coexistence solutions are currently being investigated, at both physical and MAC layer. In this work, we explore the impact of a MAC-layer solution that is supposed to allow graceful co-channel coexistence, finding that there are indeed some cases where, depending on the choice of parameters and configuration, the performance of WiFi traffic can be seriously degraded.