Hello Kenny South,
Templates as ControlPanelInsert.ascx and ControlPanelEdit.ascx are used in versions before 3.6. This means that you are using the old implementation. Anyway you could check the following.
1. Make sure that the name of your metakey is the same as the ID of the control you use to persist the data.
2. Make sure that you have added your contol inside ContentMetaFields
the Telerik team