Hi Joe,
It was a problem with my Calendar template (missing closing div), and it’s been fixed.
Thanks for your prompt help!
Yes, I’m using a child theme of Twenty-twelve.
Haven’t altered any of the plugin code to affect the sub-details div.
Its strange I’ve used this template and plugin combination before (just not on wp 3.5.1).
I’ve temporarily opened up the site so you can check it out:
http://dev.relishhost.net/casa/for-parents/calendar/
There are multiple events on March 14 and 15th (so you can try by clicking the one visible and then see the others appear).
That is what I thought also, but none of my 10 events has ANY HTML. they are all just text. I just double-checked them for unsafe characters also.