Since March 3 at least, the formatting of calendars has changed in the edit page. I have tested it across several browsers and devices, and it's the same across all of them. I am not the only person this has happened to.
Hey, thanks for reporting. I'm not sure what exactly changed in the formatting, but we haven't updated the current Calendars in a long time - but we are currently working on the next version of Calendars which will a lot more stable, so keep an eye out for this update soon!