RES wilting and twisted leaves

Hello all,
Last year, I had a nice clump of RES that grew well in a pot. Without replanting them, I left them in the same pot outdoors over winter (Germany). Over the past four to five weeks, the leaves at first began shooting through the soil and they looked pretty good to me. Then a few of them dropped and wilted, some twisted a bit and others began to blotch here and there. I suspectd “something wrong” and pulled out all of the bulbs. All felt soft and mushy, so I threw them away. My questions are:
1. What probably happened?
2. Was it wrong to have not lifted the bulbs after they went over last year and not to have replanted them last fall?
3. What should I do with the soil in the pot? Is it “spoiled” and do I have to get rid of it? If I do get rid of the soil, can I use the pot again, with or without what kind of special treatment?
Thanks for the help.
Niels