I also had the exact issue in Bug CSCvc16445. I've installed this driver and it works again:
http://support.lenovo.com/us/en/products/Laptops-and-netbooks/ThinkPad-T-Series-laptops/ThinkPad-T540p/downloads/DS102043
Thanks
When we use our SX and C series for audio calls the cameras come out of standby. Is there a setting to keep cameras in standby during audio only calls?
