From the original motion picture "Devyatayev“!Out Now: https://tilllindemann.lnk.to/LubimiyGorodLyrics by Yevgeniy Dolmatovsky Music by Nikita Bogoslovskyhtt...

This has been a bug for at least a version or two: draw a shape, go to transform it in the Properties panel, and even though the "Maintain width and Height Properties" icon indicates "not constrained", adjusting one of the dimensions adjusts the other proportionally. This seems to happen only in a fresh file (perhaps fresh launch of Illustrator), and once I click and unclick the Constrain button once, it doesn't recur in that session.  

https://www.dropbox.com/s/u0gqadn2lezzq7n/Constraint%20bug.mov?dl=0

So in the screen grab above, I draw a box freehand, then in the Properties panel, begin adjusting the height with my arrow keys. You can see the icon to the right indicating width and height are not locked together, but still, as I adjust the height, the width changes in proportion.  

Note also that once I click that icon to specify "Constrain," then unclick it back again, now I can adjust the two parameters independently. And from then on in the file, the bug doesn't recur.