Potatoes rotting

 I dug up some of my potatoes.  It’s been four days now and quite a few have rotted. Mainly the small ones. Is this normal or have I done something wrong?
I dug them up when the weather was wet and I washed them straight away. I then left them in the kitchen for two days to dry. I then put them in one of those natural fibre sacks. I put the sack in a dark place.
I have now removed them from the sack and left them out side, on a table, for the skin to harden. Obviously I can’t leave them out too long as they will turn green.

kestral , arron pilot and red duke of york. egg size and slightly under. all are affectd but the arron pilot more so. water comes to the surface of the effected potatoes and and the smell is of rot and yeast.

the leaves had spots on them. the site manager said it was magnesium deficiency.
I put epson salt.

I've got some Kestrel in a paper sack in the garage.  We just dig one or two plants at a time so they are not in there long, but they look fine.  I don't wash mine before putting them in the sack, just leave them on some newspaper indoors until the soil is dry and then rub the worst off.  We haven't lifted our maincrop yet (Sarpo Mira) - I have recently bought some hessian sacks for them so I'd be interested in why this might be happening to you so hopefully I can avoid it. 

Seems a bit early for rot to have set in don't you think. I think it's more likely blight, especially if they smell revolting.

I've just dug up all my Maris Pipers because I suspect blight. The Arran Victorys seem ok, but I will watch them daily.