NotSerializableException from Crowd's query cache

With embedded crowd, we're getting the following errors in our logs. It appears that Crowd uses the hibernate query cache, but not all query keys are serializable, resulting in errors.

@400000004f0d17962735970c 2012-01-10 23:01:00,657 org.hibernate.cache.StandardQueryCache.data ERROR [store.compound.factories.DiskStorageFactory] Disk Write of sql: select this_.id as id6_1_, this_.parent_id as parent2_6_1_, this_.child_id as child3_6_1_, this_.me
mbership_type as membership4_6_1_, this_.group_type as group5_6_1_, this_.parent_name as parent6_6_1_, this_.lower_parent_name as lower7_6_1_, this_.child_name as child8_6_1_, this_.lower_child_name as lower9_6_1_, this_.directory_id as directory10_6_1_, directory
i2_.id as id7_0_, directoryi2_.directory_name as directory2_7_0_, directoryi2_.lower_directory_name as lower3_7_0_, directoryi2_.created_date as created4_7_0_, directoryi2_.updated_date as updated5_7_0_, directoryi2_.active as active7_0_, directoryi2_.description
as descript7_7_0_, directoryi2_.impl_class as impl8_7_0_, directoryi2_.lower_impl_class as lower9_7_0_, directoryi2_.directory_type as directory10_7_0_ from cwd_membership this_ inner join cwd_directory directoryi2_ on this_.directory_id=directoryi2_.id where this
.directory_id=? and this.lower_parent_name=? and this_.lower_child_name=? and this_.membership_type=?; parameters: 32769, hal-staging-access, clover, GROUP_USER, ; transformer: org.hibernate.transform.RootEntityResultTransformer@16eaa9e failed (it will be evicte
d instead):
@400000004f0d179627363734 java.io.NotSerializableException: com.atlassian.crowd.util.persistence.hibernate.GenericEnumUserType
@400000004f0d179627363b1c at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1164)
@400000004f0d179627363f04 at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
@400000004f0d17962736528c at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
@400000004f0d179627365a5c at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
@400000004f0d179627365e44 at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
@400000004f0d17962736622c at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1346)
@400000004f0d1796273671cc at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1154)
@400000004f0d1796273675b4 at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
@400000004f0d179627367d84 at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1483)
@400000004f0d1796273698dc at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
@400000004f0d179627369cc4 at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
@400000004f0d17962736a0ac at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1518)
@400000004f0d17962736a494 at java.io.ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:422)
@400000004f0d17962736b81c at net.sf.ehcache.Element.writeObject(Element.java:791)
@400000004f0d17962736bc04 at sun.reflect.GeneratedMethodAccessor245.invoke(Unknown Source)
@400000004f0d17962736bfec at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
@400000004f0d17962736c3d4 at java.lang.reflect.Method.invoke(Method.java:597)
@400000004f0d17962736c7bc at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:945)
@400000004f0d17962736db44 at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1469)
@400000004f0d17962736df2c at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1400)
@400000004f0d17962736e314 at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)
@400000004f0d17962736e6fc at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)
@400000004f0d17962736eae4 at net.sf.ehcache.util.MemoryEfficientByteArrayOutputStream.serialize(MemoryEfficientByteArrayOutputStream.java:97)
@400000004f0d179627372d4c at net.sf.ehcache.store.compound.factories.DiskStorageFactory.serializeElement(DiskStorageFactory.java:332)
@400000004f0d17962737351c at net.sf.ehcache.store.compound.factories.DiskStorageFactory.write(DiskStorageFactory.java:311)
@400000004f0d179627373904 at net.sf.ehcache.store.compound.factories.DiskStorageFactory$DiskWriteTask.call(DiskStorageFactory.java:415)
@400000004f0d179627374c8c at net.sf.ehcache.store.compound.factories.DiskOverflowStorageFactory$OverflowDiskWriteTask.call(DiskOverflowStorageFactory.java:295)
@400000004f0d17962737545c at net.sf.ehcache.store.compound.factories.DiskOverflowStorageFactory$OverflowDiskWriteTask.call(DiskOverflowStorageFactory.java:284)
@400000004f0d17962737c98c at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
@400000004f0d17962737e4e4 at java.util.concurrent.FutureTask.run(FutureTask.java:138)
@400000004f0d17962737e8cc at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:98)
@400000004f0d17962737f09c at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:206)
@400000004f0d1796273813c4 at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
@400000004f0d1796273817ac at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
@400000004f0d179627381f7c at java.lang.Thread.run(Thread.java:662)