the sloped metal roof. could be acting as a passive radio link deflection, or passive repeater
read post #4 here http://forum.tp-link.com/showthread.php?3038-Setting-up-2-x-TL-WA7510N-as-a-wireless-bridge&region=china 25mts is 75 feet

I manage to setup WA7510N in Bridge Mod but after a period of time it disconnects even using the latest firmware which they claim that they'd fix it http://www.tp-link.com/en/article/?faqid=463 but the problem still exists and worse. In my opinion your distance is incorrect. Your estimate distance is 150 ft which is 45.72 in meters while your distance configuration is 0.1 or 100 meters. It says if you misconfigure your distance this will lead to a bad connection. If your estimate distance is 150 ft just leave it 0 or change to indoor mode. See my settings here http://forum.tp-link.com/showthread.php?75261-7510N-Firmware-Issues-from-original-to-latest.&region=china

Don't use bridge mode on TL-WA7510 and TL-WA5210G.

1) Use AP + Client instead. You can enable WDS on the Client if you require transparent communication on Layer 2.

2) Use AP + Universal Repeater instead if you need WI-FI at the client side too. You can use Repeater(not universal repeater) if you require transparent communication on Layer 2.

3) Set the right distance as #2 said.

Users should have a basic knowledge of WDS and OSI if he requires for wireless transparency. And he can find "enable WDS" option in wireless menu of TL-WA7510N in Client mode.

Well, anyway, here I try to explain some details about "WDS funtion" and layer 2.

Although 802.11 WLAN is very different from wired Ethernet LAN, it still uses the same IP protocal on Layer3. So when talking about wireless transparency, it refers to the transparency of Layer 2 (MAC Layer).

In Wireless Distribution System(WDS), like internet-----router------br_A )))((((br_B ----LAN, wireless bridge devices br_A and br_B must BOTH be able to handle 4-address-format 802.11 wireless frames in order to provide transparent communication on MAC layer. This 4-addr-capable feature often appears as "WDS funtion" on many wireless devices, including UBNT and TP-LINK.

WDS Repeater uses 4-addr format to transfer wireless frames, which provides layer-2 transparency across the wireless link. BUT It requires the root device to be 4-addr-capable.
Universal Repeater uses 3-addr format to transfer wireless frames. All devices behind universal repeater share the same MAC to communicate with the upstream network. It cannot provide layer-2 transparency but it doesn't require the root device to be 4-addr-capable. So this Universal Repeater mode is often recommended by many vendors for better compatibility.

The same reason for Client mode...

For most users, layer-2 transparency is not necessary. So if you don't know what is layer-2 transparency, then just leave the WDS option empty in Client mode or use Universal Repeater as you need.