Xperia Blog submitted a new resource: Xperia Tablet Z Wi-Fi_SGP311_10.7.A.0.222_EU1_Generic - Sony Xperia Tablet Z Wi-Fi (SGP311) Android 5.1.1 firmware - Generic EU1 Read more about this resource...
Yes, the older Xperia Z series Android 5.1 update did not fully patch the Stagefright exploit. Hopefully we will see this in the next update for these devices.