When we run PMRP for a shop order it auto transfers material from standard inventory to project inventory, however it always keeps at least 1 of each item in standard inventory. Why is that? Is there a setting I have on for the location? part? site?

For example I need qty 5 of part A. There is 5 in std inventory. I run PMRP which transfers 4 into my project and leaves qty 1 in my std inventory, and creates a purchase req for 1. 

Help?