The "memory.used" statistic on a virtual machine is returning a negative value , ie.
<statistic href="/api/vms/260f8508-2bea-4202-9b93-f8f0dcddc334/statistics/b7499508-c1c3-32f0-8174-c1783e57bb08" id="b7499508-c1c3-32f0-8174-c1783e57bb08"><name>memory.used</name><description>Memory used (agent)</description><values type="INTEGER"><value><datum>-2061584303</datum></value></values><type>GAUGE</type><unit>BYTES</unit><vm href="/api/vms/260f8508-2bea-4202-9b93-f8f0dcddc334" id="260f8508-2bea-4202-9b93-f8f0dcddc334"/></statistic>
by the RHEVM 3.2 ReST API.
while, in the Web Administration Console, memory consumption for the same VM, shows a positive percentage value.