Tenda W311R+ net droupouts when used as AP

[itm]

I have a Tenda W311R+ configured as a wireless access point on my network. At the moment it's running in parallel with my old WAP (a Buffalo Airstation Wireless-G), and is connected to the same switch.
I have no problem connecting devices to the W311R+ and getting access to LAN or internet resources, but from time to time the wireless devices connected to it lose internet connectivity. I need to disconnect them and reconnect them to the W311R+ to re-establish this connectivity. This happens with both a Samsung Q330 laptop and an HTC Desire Z smartphone, which are the only wireless devices connected to it.
Does anyone have any idea what might cause this sort of behaviour?

 

[itm]

It seems that wireless devices are losing both LAN and internet connectivity. Neither can be restored without dropping and re-establishing the wireless connection to the Tenda access point.
???