If a calendar on the server was created by DAVx5, deinstalling DAVx5 seems to throw away the calendar on the server as well as on the Android device. Android does warn you that all the application’s data will be removed, but I wouldn’t expect the calendar on the server to be removed as well. Even if the calendar itself was created by DAVx5, the data in it may have been created by an application on the server. Fortunately I’m paranoid and exported a copy of my calendar first, but this could be a nasty trap for the unwary user. Of course people won’t normally be deinstalling it, but you need to if you want to switch between the release version and a debug version built from the sources.
The workaround is to switch off the server (or the connection to it) before deinstalling DAVx5, or of course to export your calendar first.
Seen with DAVx5 Version 2.1-ose built 1 Jan 2019