Subform opening with previous filter - ms-access

Question

I've created a main form with a subform on it. The subform is filtered using a couple of combo boxes and command buttons on the main form.
For some strange reason when the form is closed and reopened, the subform is already showing as if it is filtered.
The method I'm using to filter the subform is to build an sql string that will be used as the subform's recordsource when a command button is pressed to apply the filter.
Here's the function that builds that sql string:
Public Function strSfaPaymentRecordSource() As String
strSfaPaymentRecordSource = "SELECT " _
& "[tblSfaRemittances].ID, [tblSfaRemittances].[SfaBudget], " _
& "[tblSfaRemittances].[PfrFundingLine], [tblSfaRemittances].[ContractNo], " _
& "[tblSfaRemittances].[LedgerDesc], [tblSfaRemittances].[TransDesc], " _
& "[tblSfaRemittances].[Period], [tblSfaRemittances].[Amount], [tblSfaRemittances].[Memo] " _
& "FROM tblSfaRemittances"
If Me.cboFundingLine > "" Or Me.cboReturnPeriod > "" Then
strSfaPaymentRecordSource = strSfaPaymentRecordSource & " WHERE"
End If
If Me.cboFundingLine > "" Then
strSfaPaymentRecordSource = strSfaPaymentRecordSource & " PfrFundingLine = '" & Me.cboFundingLine & "' And"
End If
If Me.cboReturnPeriod > "" Then
strSfaPaymentRecordSource = strSfaPaymentRecordSource & " Period = '" & Me.cboReturnPeriod & "'"
End If
If Right(strSfaPaymentRecordSource, 4) = " And" Then
strSfaPaymentRecordSource = Left(strSfaPaymentRecordSource, Len(strSfaPaymentRecordSource) - 4)
End If
End Function
And then the command button assigns the subform recordsource to the above string function:
Private Sub CmdApplyFilter_Click()
Me.frmSfaRemittances_sub.Form.RecordSource = strSfaPaymentRecordSource
End Sub
Now though, whenever I open the form, the subform is already filtered the same way (even if I filter it another way, close the form and come back to it).
I've checked the subform's recordsource and there is no WHERE clause saved there. I've also ran Debug.Print on the subform recordsource when the form and subform opens and still there is no WHERE clause being applied.
There's no code running on the any of the form or subform.form events, so I'm kind of at a loss as to why it's behaving this way. Any pointers would be appreciated :)