free slack changes when i paste from fixed cost to cost1 column

[ketanco]

My schedule is based on a previous similar project, where I had copied the file, renamed it and made all necessary adjustments to durations relations and inserted and deleted activities etc…. now I am about to assign lump sum costs. Also in the previous jobs schedule, I had assigned fixed costs to activities, and now those fixed costs are still like the old projects costs. Now I will erase all the fixed cost column and will enter costs from scratch. However before doing that, in order to still see the old costs, I inserted a new cost column, cost1, and I started pasting the old costs to that one, so that when I erase the costs in the fixed cost column, I still see them on the side and can get a reference point in my head. But a strange thing happened when I pasted from fixed cost column to cost1 column and for some reason the free slacks of just some of the activities changed. I could not make any correlation as far as they are the new activities or old ones or summary or critical or what else….. just some activities free slack changed, although only thing I was doing was pasting from fixed cost column to cost1 column. Why did this happen and how can I prevent it? All my purpose is to paste the old job’s costs into cost1 and delete everything else and start assigining lump sum costs to my schedule. Note: I checked the resource sheet and there is nothing in there, as all I did was to assign fixed lump sum costs anyway…