The introduction of High Speed Downlink Packet Access (HSDPA) in conventional WCDMA systems according to the UMTS standard will enable packet-switched broadband services with data rates of several Mbps. Until the deployment of High Speed Uplink Packet Access (HSUPA), the uplink traffic will be handled by conventional Dedicated Channels (DCHs). While the HSDPA downlink shared channel (HS-DSCH) is accompanied by fast feedback signaling channels, all feedback signals related to the uplink DCH, such as ARQ status messages, have to be transmitted via the downlink HS-DSCH. In this paper, we argue that the downlink HS-DSCH is subject to unpredictable delays, causing malicious interference with uplink protocol mechanisms, such as the ARQ. Eventually, we show how this degrades the overall end-to-end perfomance, and we propose and evaluate mechanisms how to alleviate this problem.