To perform Kasamatsu vaults, the gymnasts do not execute a complete round-off over the table. Instead, they should repulse the table sideways and continue twisting. Observe in this slow motion example how the gymnast leaves the table sideways. By the time he stands up vertically, he is already facing away from the table.
Gymnasts having problems with leaning the shoulders back out of support and turning over in one body unit for under-shoot dismounts, may benefit from learning how to make a complete back hip circle without having any momentum from a cast.