Syntax error in the item date with caldav

I noticed this new behaviour on my calcurse. Periodically it shows this message and stops working until I remove the line, but the line keeps coming back and so the problem. 

```
io.c: 543: /home/xx/.calcurse/apts:77: syntax error in the item date

```

The calcurse is running on a RaspberryPi 4 and Raspbian 11