Updating Habit Removes Previously Scheduled Events

1. I have a habit with no fixed start time (going to the gym that day without specific time)
2. I manually schedule a habit entry (on that day, specify the time for the habit/schedule it in the calendar)
3. When i update the overall habit (e.g. change the duration), all previously scheduled entries are set to no start time again. So i loose the manual set time.

I expect changes only to apply to future habit entries and not to previous ones. It would be better if it was kept to not reset/lose that information.