I'm doing some anecdotal testing of my forex strategy in my paper account. I purposely put on the worst positions. Sure enough, after several weeks I had a full load on and the market continued to move against me. Finally, after a few friendly warnings, the availble margin went negative and ib liquidated. the nice thing was, instead of closing me out, they just simply bought a small amount of one of the crosses I had created. It was very convenient. When the market turned, all I had to do was close out the long cross, and it never messed with my original systems position sizes.