Comparing this bar with its counterparts, bar 74 and 241, one can ponder whether Chopin did not commit a mistake by adding a 
to the bottom note of the 1st quaver, which changed it from b
1 to b1. This was the opinion of, among others, the majority of the editors of later collective editions of Chopin's works. A mistake consisting in writing two identical accidentals instead of different ones to simultaneously played notes can be assumed, e.g. in the Mazurka in A minor, Op. 59 No. 1, bar 112 (c1 instead of c
1). The fact that the A notation is free of mistakes is proven by the 
restoring b1 at the beginning of the 2nd half of the bar. It is also worth mentioning that if Chopin wanted to have a b1 note here, he would not have had any reason to write any accidental to this note. Except the misleading orthography – b1 instead of c2 – this version is perfectly correct, harmonically speaking, since the accompaniment in the 1st half of the bar is based on a ninth chord with a minor c1 ninth. Such enharmonically mixed notation is not unusual in Chopin's pieces, cf., e.g. the Ballade in G minor, Op. 23, bars 156-157 or the Concerto in E minor, Op. 11, II mov., bar 78. There are also many examples in which Chopin cares more about the convenience of reading, e.g. natural size of intervals (in this case a third, and not a second) or other factors, than the harmonic accuracy.
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category imprint: Differences between sources
issues: GE revisions
notation: Pitch