I'm not sure if this is a bug or expected behaviour, but reporting it as a bug anyway.

If you add an image to a post and set the size of that image to anything other than the default, it breaks out of the block. The image displays as expected on the front end (sized accordingly)

Here's an image that was dropped into the editor:

If I open the block options and change the dimensions:

The image has now broken outside of the block:

Pressing 'reset' on the image dimensions brings the image back inside the block.

Expected behavior
The image to stay inside the block

Mac & Chrome