In Android 4.4, change were made to the underlying WebView (
http://developer.android.com/guide/webapps/migrating.html) component used by the Psiphon browser. The technique used to set the HTTP proxy for this component silently fails with the new implementation on Android 4.4. As a result, the embedded browser silently fails to use the Psiphon tunnel.
We are investigating fixes for this issue. In the meantime, users are advised to use whole device mode on Android 4.4.