Difficulty Modifying/Inserting Records in Persist()

I am new to Acumatica development. I am currently working on creating a Screen (and corresponding Graph) that interacts with PR objects.

One of my first tasks is to insert a new PR Employee based on the data of an existing EPEmployee. I have overridden the `Persist()` method and based my logic largely on the `InsertForImport()` method in `PX.Objects.PR.PREmployeePayrollSettingsMaint` .Relevant parts of my graph follows:
 

using System;
using PX.Data;
using PX.Data.BQL.Fluent;
using PX.Objects.PR;
using PX.Objects.GL;
using PX.Objects.EP;

namespace PRImport
{
    public class PRImportNew : PXGraph<PRImportNew>
    {

        public PXSave<PREmployee> Save;
        public PXCancel<PREmployee> Cancel;
        public PXInsert<PREmployee> Insert;


        public SelectFrom<PREmployee>.
          InnerJoin<Branch>.
            On<PREmployee.parentBAccountID.IsEqual<Branch.bAccountID>>.
          Where<MatchWithBranch<Branch.branchID>.
            And<MatchWithPayGroup<PREmployee.payGroupID>>>.View PayrollEmployee;
        public PXFilter<CreateEditPREmployeeFilter> CreateEditPREmployeeFilter;

        public override void Persist()
        {
            var epGraph = PXGraph.CreateInstance<EPEmployeeSelectGraph>();
            EPEmployee employee = epGraph.Employee.SelectSingle(CreateEditPREmployeeFilter.Current.BAccountID);
            if (employee != null)
            {
                Caches[typeof(EPEmployee)] = epGraph.Caches[typeof(EPEmployee)];
                PREmployee prEmployee = PayrollEmployee.Extend(employee);
                prEmployee.EmployeeClassID = CreateEditPREmployeeFilter.Current.EmployeeClassID;
                prEmployee.PaymentMethodID = CreateEditPREmployeeFilter.Current.PaymentMethodID;
                prEmployee.CashAccountID = CreateEditPREmployeeFilter.Current.CashAccountID;
                // var res = PayrollEmployee.Insert(prEmployee);
                PayrollEmployee.Update(prEmployee);
                base.Persist();
            }
            else
            {
                throw new Exception($"Employee not found! Account ID {CreateEditPREmployeeFilter.Current.BAccountID}");
            }
        }


    }
}

Whenever I attempt to insert a record (using the `CreateEditPREmployeeFilter` object), I receive the following error:

```
Error: Inserting  'Employee' record raised at least one error. Please review the errors. Error: 'Legal Name' cannot be empty. Error: 'Employee Name' cannot be empty. Error: 'Employee Class' cannot be empty. Error: 'Department' cannot be empty. Error: 'Default Location' cannot be empty. Error: 'Sales Account' cannot be empty. Error: 'Sales Sub.' cannot be empty. Error: 'Cash Discount Account' cannot be empty. Error: 'Cash Discount Sub.' cannot be empty. Error: 'Expense Account' cannot be empty. Error: 'Expense Sub.' cannot be empty. Error: 'Employee ID' cannot be empty. Error: 'Class ID' cannot be empty. Error: 'Payment Method' cannot be empty. Error: 'Cash Account' cannot be empty.
```

However, looking at the `prEmployee` object at the `PayrollEmployee.Update(prEmployee)` line, I see that the the employee is properly populated with these values. Based on my limited experience with Acumatica, it seems that the code in `base.Persist()` is not recognizing the object in the Cache as inserted/updated.

I have tried using both `PayrollEmployee.Update()` (based on the `InsertForImport()` logic in `PX.Objects.PR.PREmployeePayrollSettingsMaint`) and `Insert()`, but both resulted in the same error. `Insert()` returns null, but I receive no errors from that particular function().

Looking at `PayrollEmployee.Cache` it looks like the Inserted value is not correctly populated  (only select fields shown):

     AcctCD    null    string
        AcctName    null    string
        BAccountID    -2147483647    int?
        DedSplitType    "PRO"    string
        DefAddressID    null    int?
        DefContactID    null    int?
        DefLocationID    null    int?

However, the Updated property looks to be correctly populated (only select fields shown)::

        AcctCD    "EP00000006"    string
        AcctName    "Todd Bloom"    string
        BAccountID    2896    int?
        ClassID    "EMPHOURLY"    string
        DedSplitType    "PRO"    string
        DefAddressID    3207    int?
        DefContactID    3209    int?
        DefLocationID    3131    int?