It may not be. 1100gms of Potassium Hydroxide will dissolve in a litre of water, at 25C that rises to 178g at 100C.

So are the two figures written in different ways - If you start with 1 litre then that will dissolve 1000g but the final volume will be more than a litre, or conversely that a 1 litre saturated solution of Potassium Sulphite will contain 655g ?

Either way something sounds strange because 380-400 gms of Potassium Sulphite should dissolve fairly easily in water.

Potassium Sulphite is a slightly better antioxidant than Sodium Sulphite and is used as a anpreservative and anti-browning agent in the food instry.