When creating a simple task (duration 1h) and assigning a worker that costs 100 per hour, the total cost is 100. When assigning additionally required material at cost 10 per piece, the required time drops to 30 minutes and the cost to 55 as if the material was a worker.

- reproduce
create two resources, one material (cost 10), one worker (cost 100)
create a task w/ 1h work and assign the two resources to it (100 percent)

- expected result
the duration of the task is 1h, the cost 110

- actual result
the duration is 30 min, the cost 55

- note
I used planner 0.14.4 on Kubuntu 11.10