Queue memoryLimit parameter and weird behaviour with persistent messages (AMQ 5.10.0)

Hi:

I'm using AMQ 5.10.0 and I'm trying to understand some behaviour about
destination memory limits
and how messages are managed in queues by AMQ

I've defined a persistent broker ( kahaDB ) with

<policyEntry queue=">" optimizedDispatch="true" producerFlowControl="true"
memoryLimit="100 mb"/>

and

<storeUsage>
<storeUsage limit="500 mb"/>
</storeUsage>

My test tries to send 2000 messages (1MB). They are persistent messages.
And *there isn't any consumer reading messages-*
The result is that in the 249th ( it's not a fixed number after several
tests), control flow is activated

2014-09-06 13:19:11,246 | INFO | Usage Manager Memory Limit (104857600)
reached on queue://foo.bar, size 249. Producers will be throttled to the
rate at which messages are removed from this destination to prevent
flooding it.

My questions are:

- why does AMQ need 100MB in memory to manage persistent messages ? There
isn't any consumer , so all messages should be stored into disk ( up to
storeUsage limit, ie, 500MB)

- if the test sends non persistent messages, when the 100th message is
sent, temporary store is activated ( up to tempUsage limit )
Why are the non persistent messages swapped to disk and memoryLimit looks
not be a problem if there is disk space enough, but persistent messages
require memory despite there is disk space enough?

Thanks and regards