If you close and re-open the tab everything is fine. If you switch to another tab and then back, things are fine except for the tab's icon and title in the tab bar.
Looking closer, this is caused by a load order issue where
TodayPane.updateDisplay gets called before
TodayPane.onLoad, and so
TodayPane.paneViews is still null.
The attached patch improves things but does not fully solve them. With the patch only the left hand sidebar (with the minimonth etc.) is blank rather than the whole tab's UI being off.
I've looked briefly at an approach of calling
TodayPane.onLoad if needed when
TodayPane.updateDisplay is called, but
onLoad is async and
updateDisplay is not. So you end up having a domino effect of switching functions from sync to async.
I also tried calling
ltnOnLoad near the top of
OnLoadMessenger, but that did not fix the problem.