Calender not synced / multiplied when disabled

[6heads]

Using Etar with Davx. Latest Google Play versions.

The calendars are hosted on owncloud.

My wife uses her calendar and get some shared from me.
This works well for all calendars, except the marked one. It's not visible although details tell me that it was last synced today.
I tried dis- an reenabling it, but then it began multiplying as can be seen in the screenshot.