Shift and Alt won't work together while transforming

Hi all,

I have a weird issue, I think I'm missing something very easy but can't find what.

For years I've been using shift+alt to resize an object  transformation anchor in the center and keeping proportions intact. But recently it's not working anymore.

It's either centering the transform anchor (alt) or keeping the proportions (shift), whichever I pressed later, but not both at the same time.

Any one has a clue?