Q:

Illustrator CC 2017 reset bounding box missing on square

I can't find the reset bounding box option, thing that I was able to do in the previous versions of Illustrator when building an arrow head. I am not looking for a different method on how to make an arrow head but only to understand why I'm not able to see the reset bounding box option.
In a nutshell:
after building a square and rotating it by 45˚ I was right clicking on the square and clicking on the reset bounding box option.
 
I was using this method so I could scale relative the rotated square shape on a vertical axis. The reset bounding box appears only if I move one of the anchor points.

I hope this is clear enough, if not let me know if you need any other information.
Cheers

A:

When you rotate a shape in Illustrator CC 2017, it remains a live shape. Once you convert the shape to a path (such as by moving an anchor point, as you mentioned), the rectangle ceases to be a live shape and you will be able to reset the bounding box. At this point, you lose the benefits of the live shape (editing rounded corners, for example).
When you first draw the shape, you can expand it (Object -> Shape -> Expand Shape) to regain the Reset Bounding Box command.

