Workaround 1: Try to update not a field of an underlaying query or table, but a field of the form's Recordset. For example:
With Me.Recordset .Edit !MemoField = "TEXT ADDED HERE <- " & !MemoField .Update End With
Workaround 2: If you need to update not form's Recordset, but any other Recordset, try to unbind the TexBox, make the update and then make the TextBox binded back again.

Workaround 1: Try to update not a field of an underlaying query or table, but a field of the form's Recordset. For example:
With Me.Recordset .Edit !MemoField = "TEXT ADDED HERE <- " & !MemoField .Update End With
Workaround 2: If you need to update not form's Recordset, but any other Recordset, try to unbind the TexBox, make the update and then make the TextBox binded back again.