When double clicking an SVG to reset it, the size of the parent becomes fixed and later resizing the SVG doesn't resize the parent.  

So I've been digging in the history and I found some interesting things (newest to oldest):

Removal of re-sizable SVGs:
https://github.com/ipython/ipython/commit/31398d591904b1cbe9523a9b5b1b47275568f836#diff-06df819eb26127c4e146349c7210ba2c

Addition of re-sizable SVGs:
https://github.com/ipython/ipython/commit/4e0ef097c191a46d2ce1aed28bcddef691e7c888#diff-06df819eb26127c4e146349c7210ba2c

The resizing of the parents along with the img itself was added here:
https://github.com/ipython/ipython/commit/d4e373a28b65800660b43b362eb6d4f52ba26b41