My photoshop seems to have reversed to the old version where you had to hold shift down in order to keep the image's constraints. I've heard that this can be controlled by ticking off the "Use Legacy Free Transform" under Preferences>General, however, I've tried both ticking and unticking with no success.
I agree with the suggestion from Chuck Uebele to reset your preferences. Look for the Reset Preferences On Quit button within the General tab of the Photoshop Preferences. Having done so, try the Use Legacy Free Transform option again.