The missing slur over the top voice must be a mistake of GE1 (→FE→EE). However, it may not be a common oversight, but an atypical example of a transfer of sign: a slur was printed under the notes instead of over them, although of the same range, which gave it a form of a tie of f1 (the engraver could have been encouraged to perform such a change by, e.g. lack of space under the notes).
Compare the passage in the sources »
category imprint: Differences between sources
issues: Errors in GE, GE revisions
notation: Slurs