I got a call from a customer who reported
"…a few of our meeting sites we noticed that there are several but not all meetings in March that are recurring meetings that are showing up twice yet the second link is not active."
I go to the site and sure enough, some (not all) of the dates were duplicated. "Strange," thought I…
Then it hit me: DST! The duplicate entries started after 7 March and end with 28 March.
SharePoint responds to the change with double entries to cover both time zones because its not ready to change yet. Since I knew that the patch had already been applied to the servers, SharePoint must have gotten confused somehow.
The good news/bad news is: it’s only for three weeks.