On history enabled tables a change to a type II field creates a new record. When that change is from null to a value, however, it might not make sense to create a new record.
In version 17.5 we have added an option on the table level, “treat type II as type I when field value is null”. When you enable this, the Jet Data Manager will not create a new record when a type II field changes from null. Instead it will update the value of the type II field as if it was a type I field.