Android devices sometimes use wrong DNS server. My assumption is, that it happens when device finds friendly WiFi access point, disconnects from mobile provider/ISP and is just finished connecting to it (WiFi using DHCP). It has setup DNS servers from WiFi, however, it still sends requests to DNS from mobile ISP via WiFi network.
It seems that some caching is going on, and it feels wrong… because mobile ISP may be blocking DNS requests from other networks.
Tested on Galaxy Tab 8.9″ with Android 3.2 and Galaxy Note 10.1″ with Android 4.0.4.