Describe the bug
Centering this block in the editor shows correctly in the preview, but on the front-end it is still left-aligned.

Right-aligning the block in the editor does not right-align it in either the editor preview or the front-end.

This block seems to get the class aligncenter added to it regardless of the editor settings.

To Reproduce
Steps to reproduce the behavior:

1. Add a Latest Comments block
2. Center it and publish the post
3. Note that it is centered in the editor, but not the front-end
4. Right-align it and update the post
5. Note that it appears left-aligned both in the editor and the front-end

Expected behavior
Alignment options should work and the front-end view should match the editor preview.

Screenshots
Centered in editor:

Front-end display:

Right-aligned in editor:

CSS in inspector:

Desktop (please complete the following information):

• OS: OSX
• Browser: Firefox