Microsoft has released a fix for problems occurring in Windows Mobile driven phones ( Versions 6.1 and 6.5 / HTC or Samsung drivers, such as the Sony-Ericsson Xperia X1 mobile device ) which is related with GUI Interactions. However they state that this fix might not be for everybody so make sure you do check for symptoms mentioned here.
Symptoms : Some graphical user interface (GUI) interactions no longer work correctly.You cannot answer calls when the device is in sleep mode. This issue is most likely to occur when a device is in sleep mode and has VPN enabled or when a device is in sleep mode and has active downloads.
Cause : Certain drivers do not respond correctly.
Download : You can download the fix from here.
In order to install it make sure you have connected your phone through USB and then run the setup. In case your dont have it, you can email this fix and then run the setup after downloading it locally in your mobile. Good part is that you dont have to restart the device after installation. Thanks Vasudev