This cultivar appeared on a list from the Hosta Library. It is a  sport of H. 'Mabel-Maria Herweg'. The green foliage has creamy white marginal variegation with some leaves showing streaked variegation. 'Unstable Mabel' is a small to medium size plant with  leaves that are slightly rippled, moderately corrugated, broadly ovate and have a glaucous bloom on top.

This is a sport of H. 'Mabel-Maria Herweg' which is a cultivar that is supposed to be a streaked plant. However, it often "stabilizes" into a plant with marginal variegation which has been named H. 'Stable Mabel'. It would seem that 'Unstable Mabel' is somewhere in between those two by having some streaked leaves and some with marginal variegation. Seems as if there should also be an all-green version of this hosta too.