I was playing bass in a band and we started working up "Tall Ships" by Show of Hands.

The guitarist capo'ed at the third fret and played F, G and Am shapes, hence playing Ab, Bb and Cm.

I fluffed and forgot about the capo so played F and G as bass notes before I caught on and played the C correctly. The result was Fm7, Gm7 and Cm, which was rather appealing so we kept it as an variant harmonisation.