I added a TP-Link AV200 Nano and two AV200 WiFi extenders to my home network. It now consists of the cablemodem/wireless access point connected by an ethernet cable to the AV200 Nano and two other wireless access points on the powerline network. Every access point has the same SSID, WPA2 key, and channel.
I have three laptops, a Sony Xperia TX android phone, and a Nexus 7 that all work very well connected to any of the APs.
I also have a Motorola RAZR HD that works well when connected to the cablemodem's AP, but not the powerline APs. The behavior is weird. This phone shows a strong connection to the wireless network that never cuts out, but there is extremely high packet loss. I've tested with both powerline APs separately. I get the same results.
I have made sure that the TP-Link devices all have the latest firmware. The problematic phone has been tested both with Cyanogenmod 10.2 and 11.
How can I further diagnose this issue? It seems weird that the phone appears to have a good wireless connection, but network traffic has problems.