Also, if it's any use, below is the Record Source for the subform:
SELECT DISTINCT dbo_POHeads.ID, dbo_POHeads.OrderNo, dbo_POHeads.Supplier, dbo_POHeads.OLDID, dbo_POHeads.Removed
FROM dbo_POHeads LEFT JOIN dbo_POLines ON dbo_POHeads.ID = dbo_POLines.POHeadID
WHERE (((dbo_POHeads.Removed) Is...