I have the exact same problem. My "contract" campaign that needs 85% of all impressions gets 50% (set at a weight of 10 + # of impressions) and my "remnant" campaign set at a weight of 1 is getting 50%, when is should get 15%. I will seriously be undersold for the contract campaign (paying customer) and oversold for the remnant (freebie). If I remove the remnant, I get white space in between the ads of the contract campaign. Seems to be a major issue.