Meanwhile I checked the pattern you shared. This does not seem to be a bug based on those rules.
The event is set up for Monday to Thursday to start at 5:30, then another recurrence is set up for April 10 at a different time. Obviously this will result in the event showing up twice on that day.
At the moment the result what you would like to achieve is not possible with our plugins.
What you could do is set up the event with the following rules:
- weekly Mon-Fri 5:30
- weekly Sun 6:30
Once that is done, then break out the event on April 10 from the series and set the starting and finishing time according to your needs.
This way the event on April 10 will not be part of the series, but it will show up only once and at the right time.
Cheers,
Andras