Share your experience!
When I'm in a call and switched to another app, they keyboard and touching on the app does not work. Only scrolling works.
Anyone is facing the same issue?
Solved! Go to Solution.
On my phone it was the same. Unable to multitast during a call.
The solution is to uninstall "SmartKey" app from Sony. This is the application which is blocking the multitasking function.
Not sure when Sony will fix this application.
Hope this helps.
If everything works fine in Safe Mode means yhis issue was indeed caused by SmartKey app.
Managed to fix the issue by uninstalling this app...
Thanks VikramSG
I have received more information about Smart Key and this issue and i'm afraid it will not be possible to solve this issue. Smart Key works by creating an overlay to intercept headset actions. When this overlay is shown the Android system can't know when you want to fill a text field which is why you can't see the keyboard during calls.
We will release a new version of Smart key that gives a dialog with information about this when you enable Smart Key though but to use the keyboard during calls you need to remove/disable Smart Key.
I am also getting the same issue on my Xpreia L after updating the phone.
How to resolve this..... I have a smart phone without smart features. 
If you want to keep the SmartKey app installed you can also turn it off for calls. To do this, open SmartKey and then move the slider next to "CALL" to "Off".