iPad connects to WPA2 but not to WPA ???

My new iPad, with updated new iOS 4, does not connect to the Wi-Fi using WPA-PSK TKIP. The pasword is 100% correct. Strange enough everything works fine using same password and WPA2 -PSK. How is this possible? How can I fix this? I need WPA-PSK TKIP, because my laptop connects only using WPA but not with WPA2. My other devices alos don't have any problem with my WPA settings. What is wrong with the iPad settings?