It cannot be ruled out that Chopin indeed envisioned the entire four-bar section being performed with one pedal, in spite of the harmonic change in b. 21. It would emphasize the unifying function of the ostinato, quartal mixture in the bass. On the other hand, it is that very constant bass motif that could have confused Chopin, who, while adding pedalling markings (in haste? – cf. the erroneous pedalling markings in the Prelude No. 19 in E
Major, b. 26-27), could have been following the bass line only. Due to the above reason, in the main text we suggest a possible pedal change at the beginning of b. 21.
In FC and EE there is no 
following 
in b. 18 at all, while GE overlooked also the mark, as a result of which b. 18-22 are devoid of pedalling markings.
Compare the passage in the sources »
category imprint: Differences between sources; Editorial revisions
issues: Errors in GE, Errors of FC
notation: Pedalling