Wi-Fi cutting out randomly

I have a strange one. The inbuilt Wi-Fi works perfectly with my WPA-enabled D-Link router, authenticating automatically in seconds. However, if any power saving mode is enabled, the Wi-Fi cuts out without any indication (The Wi-Fi still shows green in iPAQ Wireless) in around 2 minutes. Any Net activity just stops on the device. I've tried resetting both router and hard-resetting the device but no avail. This seems to happen at any distance from the router.

HP rx4240 with 1GB SD card and Holux GPSlim240