Water in bedroom ceiling again

Well we got back from a long weekend away from the house and I noticed a bubble in the bedroom ceiling. I poked at it and sure enough it was full of water. I drained it and let it dry out. Went up into the attack last night and looked around and found no leak in the roof or around the furnace vent pipe. I have no idea. Only thing I can think if is I needed to put some more insulation in that area so I did. It might have been a bit thin on insulation right in that area because that is where we had a leak last year. The insulation had been moved around and was not at tall at the other areas. So I put some of the extra insulation I had in the basement down and put a few sheets of it across the top also. Hopefully that will help me show where if any water is leaking through the roof. Hopefully it was just because there was not very good insulation in that area and it was just making some of the cool air condense and water was pooling up.