The reason you might gain some weight after eating starches is that starch contains a lot of insoluble fiber (for eg. a potatoes fiber consists of 52 % insoluble fiber) wich makes you bind water and fat so you might look puffier and heavier, eventhough you didn´t gain an ounce of fat, cause water weighs more than fat.
and if you still feel fat cells (those little rolls) under your skin it´s either cause the water retention didn´t appeared as ussually edemas do over them but below them or cause the water cells resuspended the fat cells and made them seem bigger
but that state of puffiness is only a defending mechanism your body does to keep away the toxins of the cooked starches (starches aren´t toxic but cooking kind of is...) of your cells. This mechanism is similar to the one that happends when you have to much sodium in your system.
so starches do not make you fat as long you don´t add any fat to it and keep it vegan of course ;)