The traces visible in FE prove that, originally, the top voice was led differently: 
. It is the slur, removed at the time of that proofreading, that particularly draws attention – one can ponder whether it was not supposed to be adapted to the new shape of the melody and not to be removed. However, uncertain as to the range of a possible slur, we do not suggest any addition.
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category imprint: Corrections & alterations; Source & stylistic information
issues: Authentic corrections of FE, Main-line changes
notation: Pitch