This is not a bug, this is a feature. HOX used to come up with a pop-up window asking what type of connection you would make, charge only, or USB device.
Instead it now uses a HTC-defined default USB connection method.
You SHOULD, however, be able to see the device in explorer. If not, check in Developer Options and try USB Debugging, see it that makes a difference.
Only other thing I can think of is, in Hardware (Device Manager): check if OneX is available, whithout an exclamation mark.