Try Option+Shift on Mac (Alt+Shift on Windows)
It doesn't work (Or I failed). Option+Shift resize the layer, with homothetic proportions locked.
Another strange thing:
In previous CC versions, with Option+Shift, the resizing was done from the center of the layer.
Now (CC 2017.1.1), with Option+Shift, the resizing is done from the opposite corner of the layer (for example, if you click on the top left corner with Option+Shift and you reduce the size of the layer, the locked corner will be the bottom right.)
Do you know what I mean? I can't find a solution to resize a layer with homothetic proportions locked AND from the center of the layer.
ok I finally found the solution... it was a bug introduced by a wacom driver and photoshop 17.1.1.
the driver was bugged with all ALT, CMD and SHIFT key.
I updated the wacom with the last driver and it fixed the problem.
Thanks for feeding back Eddy - it may help others