Additional CSS Classes not being added to Editor

Hi,

On the Icon Block, when I add a class in the Additional CSS Classes field of the Inspector, under Advanced, the class is added to the front end, but not the Back end Editor. The same is true if I use registerBlockStyle and create a new Block Style in the inspector: the class is added to the front end, but not the backend.

The problem is that this defeats the entire purpose of Gutenberg — that the content creator actually sees what the content will look like on the front end while editing. Is there a fix for this?

I’ve run into this problem several times with other blocks, not just yours, so it seems to be a common problem with contributed third-party Blocks.