I've seen this mentioned in other threads combined with other issues, and some of those threads are marked solved, so I've started a new one.
I've upgraded with each an every upgrade over the last sevral weeks, but have only just started using the DTRegistere calendar; I was using JEvents. The month name at the top of the calendar only appears for May, June, July, of any year, and not any months prior or beyond. I realized as I was typing this that it is most likely a template issue. And for those three months, the name/year is so large that 1/3 of it is cut off. I'll report back after I modify my template.