Setting the start and end timedate in a new event sometimes fails ("end date before start date" error)

1. Start khal interactively
2. make a new event
3. set the start time and the end time (I set it normally with 1 hour difference)
4. Sometimes (like in 50%) the khal denies creating event saying "end date before start date"
5. Return to set the times normally solves the issue

OS, version, khal version and how you installed it:

• khal 0.11.3
• installation method: pip
• python 3.8.10
• Linux Mint
• Your khal config file
  `
  [locale]
  timeformat = %H:%M
  dateformat = %d.%m.%Y
  longdateformat = %d.%m.%Y
  datetimeformat = %d.%m.%Y %H:%M
  longdatetimeformat = %a %d.%m.%Y %H:%M
  unicode_symbols = true

[default]
highlight_event_days=True
show_all_days=False
default_calendar=mycal

[highlight_days]
color = dark cyan
`

Additional context

Sometimes even if the error is not shown the actual time interval is far from 1 h, but 8 hours or more.
For example, I set from 10:30 till 11:15, but when I save it, I got from 10:30 till 21:00

Start khal interactively and reproduce the new-event flow by entering a one-hour start and end interval, then compare the saved event’s times with the entered values. Trace the handling of start and end times around event creation, including the reported “end date before start date” validation. Done means repeated entries save the intended interval without intermittent errors or large time shifts.