LEAK DETECTED, after nodetool drain

ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,055 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@5534701) to class org.apache.cassandra.utils.concurrent.WrappedSharedCloseable$1@194296283:[[OffHeapBitSet]] was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,057 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@fab2c71) to class org.apache.cassandra.io.util.MmappedSegmentedFile$Cleanup@1252635616:/var/lib/cassandra/data/metric/metric-811fa5402a3b11e5a2c0870545c0f352/metric-metric-ka-6883-Index.db was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,057 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@555d8efb) to class org.apache.cassandra.io.util.MmappedSegmentedFile$Cleanup@1252635616:/var/lib/cassandra/data/metric/metric-811fa5402a3b11e5a2c0870545c0f352/metric-metric-ka-6883-Index.db was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,057 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@7b29bfea) to class org.apache.cassandra.io.util.MmappedSegmentedFile$Cleanup@1252635616:/var/lib/cassandra/data/metric/metric-811fa5402a3b11e5a2c0870545c0f352/metric-metric-ka-6883-Index.db was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,057 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@2d37dc5a) to class org.apache.cassandra.utils.concurrent.WrappedSharedCloseable$1@713444527:[[OffHeapBitSet]] was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,057 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@13153552) to class org.apache.cassandra.utils.concurrent.WrappedSharedCloseable$1@713444527:[[OffHeapBitSet]] was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,057 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@25f51e35) to class org.apache.cassandra.utils.concurrent.WrappedSharedCloseable$1@713444527:[[OffHeapBitSet]] was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,057 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@3633d3dd) to class org.apache.cassandra.utils.concurrent.WrappedSharedCloseable$1@194296283:[[OffHeapBitSet]] was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,057 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@2ec81280) to class org.apache.cassandra.utils.concurrent.WrappedSharedCloseable$1@194296283:[[OffHeapBitSet]] was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,058 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@144d1dae) to class org.apache.cassandra.utils.concurrent.WrappedSharedCloseable$1@194296283:[[OffHeapBitSet]] was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,058 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@1944bda4) to class org.apache.cassandra.utils.concurrent.WrappedSharedCloseable$1@194296283:[[OffHeapBitSet]] was not released before the reference was garbage collected
ERROR [Reference-Reaper:1] 2015-08-14 13:37:37,058 Ref.java:179 - LEAK DETECTED: a reference (org.apache.cassandra.utils.concurrent.Ref$State@31c1386a) to class org.apache.cassandra.io.util.MmappedSegmentedFile$Cleanup@1601396928:/var/lib/cassandra/data/metric/metric-811fa5402a3b11e5a2c0870545c0f352/metric-metric-ka-8229-Index.db was not released before the reference was garbage collected