There is no firewall restrition or AP isolation between the two routers.
I have a WDS (Wireless distribution system) structure built with 2 TP-LINK WR740N, that has been working great. They are under the same subnet (192.168.0.2 and 192.168.0.3).
The thing is I can't reach the second router (which gets the DHCP from the first one) when I'm connected through the first router, wireless-ly or "wired-ly". The control webpage won't open and I can't ping it, even though it shows in my network map.