So the melody note stays on its final note of Eb, the bass descends to B, which could then lower to Bb as part of a chromatic progression as mentioned above, but instead acts as a leading tone back into Cm. The addition of the Gb in the final version of the chord, making a full B chord, adds the element of strangeness, which is quite appealing.
Here's another example of a similar but slightly more complex idea, the song ends on Bm, a guitar does a D to D (the minor 3rd) octave slide over this, then the chord falls away to Bb (of which D is the major 3rd), and a different melodic motif comes in that again starts and ends on D, the last time it happens the chord underneath moves back up to Bm, with the final D melody note ringing over it. I find this kind of thing very pleasing