plants going to seed when you don't want them to

Help, The summer before last I had a plant go to seed, not viable but little white ones. My next harvest I had 3 or 3 go to seed, same kind. Next harvest all but 1 went to seed. I shut my room down and cleaned everything with detergent and started over with clones from a friend. Everything went well. Now this harvest All 10 went to seed, again the little tiny white ones. I have been growing for 8 years and never heard of this. How can I get my plants not to do it again? I scrubbed my room with bleach because I heard that might help. Any ideas would be appreciated as I can find nothing about this in any book. thanks Scotty

Maybe there's a grow nearby, are you venting from the outside?

the plant is throwing pollen on itself probably 2 weeks before harvest...its normal actually...unless you know the genetics of your seeds are VERY stable, there is probably nothing you are doing specifically wrong...its just what the plant does