As reported by Debra Dotson in MDLQA-382:

When I click on the chat link, it will show the next session date correctly (the next day or the next week depending on the settings) but the initial date still appears in the calendar. Only after I go into the update screen and click "Save" will the date advance in the calendar. (I don't have to change the date as it has advanced automatically - I just need to save it for it to appear in the calendar.) Sometimes simply clicking on the chat link as faculty will advance the date in the calendar, but not always.

The calendar doesn't seem to want to advance to the next scheduled chat time after the initial chat date/time has passed. With 1.9 it seems to update immediately after refreshing the course page.