Capacity Scheduler can hang when submit many jobs concurrently

In hadoop2.0.1,When i submit many jobs concurrently at the same time,Capacity scheduler can hang with most resources taken up by AM and don't have enough resources for tasks.And then all applications hang there.
The cause is that "yarn.scheduler.capacity.maximum-am-resource-percent" not check directly.Instead ,this property only used for maxActiveApplications. And maxActiveApplications is computed by minimumAllocation (not by Am actually used).