The only possible cause I can think of is that I use some MG 12-6-4 diluted at 1/2 stength, then on my next feeding using MG 15-30-15 at 1/4 strength. Those elements coupled with damp soil from water = magic shrooms in your Purple Ladies pot.
I would suggest using your local search engine. Not only is that completely impossible, mycelium does not feed on MG or NPK for that matter. Mushrooms arent plants. Thier spore are in the air at all times. There is almost no way to get around that. Make some agar leave it out. Within 3 days you will several species of fungi fighting for it. Repotting won't do anything, the mycelium is in the dirt. So I was asking where your at and the soil, and what not. Cuz mycology is not my field, genetics is my field. I was trying to get a true anwser, specie, function. After some minor research. Your soil seems to be the perfect place for fungi. Hardwood chips, some organic matter, and bascially topsoil. Only reason you know they're there is because it was over watered. If wasnt for a drenching lasting long then two days, generally mushrooms wont flush.