Hello. This problem is not related to KitKat update but latest Chrome update (33). I have the same issue on HTC One X. It appears after Chrome start. Killing and starting Chrome results in turning on loudspeaker on first call. Problem can be solved by uninstalling Chrome updates (and disabling auto update). Latest Chrome beta works fine.
At first I thought it was my fat face hitting the screen and starting speaker mode, then stumbled across this thread and voila! Face isn't so fat after all. It happens all too frequently to me. Sucks.
Did you uninstall Chrome or are you just not using the app?