On the Layout the Incident.CustomerOwnershipForm the placement is specified as a Panel:
This option allows the Form to be minimized or moved around the screen.
The only way to stop this would be to change the Placement setting to "tab". It will mean that the Customer & Owner information will now be on its own tab instead of above the Details:
You could create a new form that has the Customer & Owner information on the same form as the Details to get round this. This is how the information use to be displayed before the "Panel" option was implemented.