Same problem here:
New contact/lead added via a form.
Here is the data I entered in the form, which is correctly reflected in the table mau_leads. Here the data from a sql query from table mau_leads:
Date Last Active (autofilled): 2020-04-01 23:11:20
webinarzeit (custom field time): 23:30:00
webinar ziet & datum (custom field datetime): 2020-04-01 23:30:00
Opening the contact/lead in Mautic:
Date Last Active (autofilled): 2020-04-01 23:11:20
webinarzeit (custom field time): 0:30:00 => showing +1 hour
webinar ziet & datum (custom field datetime): 2020-04-02 1:30:00 => showing +2 hours
I also added the timezone to the record, no difference.
Now that the UK changed to british summer time I can also see the issue and it looks like is bug.
The edit mode binds the converted date but the display one bind the UTC one which is guess is the one saved on the database.