First of all I want to thank all contributors, board members and Oleg for this great site. This site is one of the reasons why I left NetGear and embarked on Asus board.
I had upgraded from release 5a to 6a but since WAN interface behaved erratically I had to downgrade back to 5a.
The WAN port is connected to an ISDN router over plain Ethernet 10Mbit/s. While on 6a webpages would load half way and it would take at least a couple of minutes before they opened completely. Email also stopped downloading after first few messages and it took 3 more minutes before it received the rest.
To me it looks as if there is something not working on the WAN interface either related to media detection or traffic flow control.
And surely the AP was rebooted before and after upgrades with no change in configuration settings.