I think it is an incorrect approach to use a stacked bar chart when there are negative values. I frankly don't see how the chart should be drawn. Sunny's solution shows the right numbers, but the sizes of the bars are misleading.
I would instead suggest a grouped bar chart, with an additional "total" bar (check box under "Dimension Limits")
Many thanks, also a good solution, but not helpful as we don't only have three products, but a higher amount of products, therefore there might be some graphical issues as a consequence...
Anyway, the problem is already in revision and qlik already accepted theirselves this as a "bug", maybe we see a solution in a future release of qlikview. Until then, I'm happy with Sunny T's solution.