Full day tasks get the time 0.00 o'clock

If I create an all-day task via an app or directly at the provider and synchronize it via CalDAV, it will be displayed correctly in eM-Client.
But if I somehow edit it in eM-Client, the software generates the time 0:00. The problem: All reminders (smartphone etc.) now take place at midnight! Unfortunately, this prevents me from editing the tasks with eM-Client, which is a pity.
It is also impossible to create full-day tasks in eM-Client.

Who is the calendar provider?

I use Mailbox.org. There are no problems when creating or changing all day tasks via the website or via apps that use the davdroid interface. Only once an entry has been edited with eM Client, it gets the time 0:00 o’clock.

One solution could be the option to ignore the time 0:00 in the ‘End’ field or simply omit the time in the log. I’m not sure if this helps, but here’s a sync-log. Task created via an app, eM client started, task description added, synchronized and eM client stopped. Then the time finds 0:00 o’clock on all apps.
You find a log here: https://ln.sync.com/dl/a29483f10/gymwtpm7-zs62kuji-a7c2eh2b-u976tp4q

It should be easy to test, because there is a 30d-trial on www.mailbox.org without the need of any personal informations.