Major Description
If PFC is disabled, when the store cursor checks limits, it checks only the memory percentage of its own MemoryUsage and compares it to the high water mark. Otherwise if PFC is enabled, it checks whether the MemoryUsage is "full" but the "isFull" method also checks its parents.
This issue arrises when you have memory limits set on queues higher than the overall system limit, as well as if you have multiple queues who's memory limits combined are higher than the overall system limit. These settings must be taken into account.
The original form can be found at
http://activemq.2283324.n4.nabble.com/What-can-be-reason-of-460-memory-usage-limit-td4665651.html