The problem is that the Scheduler allows you to drag an event outside the visible area of the view, the event does not disappear, but cannot be shown in the current view. If you switch to Month view for example, you will be able to see the event there.
Anyway this is a behavior that we need to improve, so I have logged this in our internal bug tracker, so it will be looked into and improved in future release.
Thanks for reporting it.
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