Mushy tatties

Just harvested my first full row of spuds (Vivaldi). Some leaves had yellowed with brown patches and I am wondering if this is a deficiency of some sort? The potatoes themselves are fine and very tasty, but I noticed that the original seed potato on every plant was either a mushy soup or there was nothing left at all but the skin!

Is this normal or should I be concerned?

Phew. 

Too late. Ew.