SUMMARY Constraint shortcuts with the Transform (e.g. uniform scale [Shift + Alt], scale from center [Alt]) can only be used after you initially click to use the transform tool. STEPS TO REPRODUCE 1. Select Transform Tool 2. Use [Shift + Alt]/[Alt] before using the Transform Tool OBSERVED RESULT Shortcut keys are not applied EXPECTED RESULT Shortcut keys should be applied SOFTWARE/OS VERSIONS Windows 7 Professional x64 ADDITIONAL INFORMATION The issue with this is that you will almost always move the image by accident before you get to push the shortcut keys. Then you have to undo to return the image to it's original transform before trying again. If when clicking the transform, Krita would check for any shortcut keys held down and apply them it would really improve workflow. It's a tiny change (probably not a tiny change in code though), but it would increase the usability of the program. I don't know if this is a bug or there is a legitimate reason for Krita to have this behavior.
To add to this, if you have grid snapping enabled and you want to uniform scale the transform (and the transform is currently close to a grid line) once you click on the transform the snap can be accidentally applied before you can use the hotkey for uniform scale (resulting in a non-uniform scale). If the hotkeys were applied beforehand then the accidental snap wouldn't matter (given that you only cared about resizing uniformly). The application of hotkeys after clicking feels 'clunky'.
While the stated behaviour is true, it is working as designed. I'll set it to wishlist.