On the RadScheduler when dragging an appointment to the all day slot the functionality does not work consistently, I have recreated this on your demo here: https://demos.telerik.com/aspnet-ajax/scheduler/examples/overview/defaultcs.aspx
Please see this video for an example of the issue: https://www.dropbox.com/s/te7eol3sls2w56l/RadScheduler%20Problem.mp4?dl=0. Between 0-3 seconds the functionality works correctly and the event goes into the all day section although it does not look correct. Between 3 seconds and 10 seconds it does not go into the all day section at all. At 11 seconds it works perfectly for the first time, and from 13 seconds onwards it once again fails to go into the all day section.