Proportion lock is ignored when scaling.
I've placed a bitmap on my page. When scaling it with the scaling tool and the proportion lock engaged, proportions aren't maintained.
Scaling with the Scale Tool scales the objects without taking into consideration the Constraint Lock icon, it works independently of the state of this icon. Only when you use the W & H fields, the Constraint icon is used.
So, it is not a bug. You can also see this work similarly in Adobe Illustrator too.
Adobe InDesign team
Thanks for the prompt response.