Pressing CTRL+LMB/RMB does not scale along the X or Y values automatically. Instead, it scales the entire object.
1. Open Editor (any project)
2. Place any object in level
3. switch to scale widget
4. Press CTRL+LMB to scale along X axis
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-12131 in the post.