Queries :: Update Query Peculiarity - Not All Fields Updated

I'm mid build on a commitments tracking (pseudo Purchase Order system) project, but seem to have run into an issue with a loop I'm building to allow users to edit commitments. The idea is that an edit form is launched, values amended and the submit button is clicked. A VB subroutine then validates the entries to ensure that the mandatory entries are included. It then writes a copy of the original values to the Archive table, before attempting to update the existing commitment with the new values..

This is working perfectly, apart from the fact that 3 fields that are "updated" are being updated to a blank value..

Code:
Private Sub CommitSubmit_Click()
Dim SQLStr, LastID, DOwner, DHeading As String
Dim ErrState, Dtype, DProperty, DTCA, DITD, DSD, DED, DSP, DRetention, DRA, DRPD, DSupplier, DDOW, DStatus, DUser, DShD As String
Dim Authcheck, Complete, ErrMsg As Boolean
Dim QDF1, QDF2 As QueryDef

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