CreateTime is reset to 0 when a partition is overwritten

hive> describe extended zshao_ttp;
OK
d       string
ds      string

Detailed Table Information      Table(tableName:zshao_ttp, dbName:default, owner:zshao, createTime:1264027720, 
lastAccessTime:0, retention:0, sd:StorageDescriptor(cols:[FieldSchema(name:d, type:string, comment:null)], 
location:hdfs://hdfs:9000/user/hive/zshao_ttp, inputFormat:org.apache.hadoop.mapred.SequenceFileInputFormat, 
outputFormat:org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat, compressed:false, numBuckets:-1, 
serdeInfo:SerDeInfo(name:null, serializationLib:org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, parameters:
{serialization.format=1}), bucketCols:[], sortCols:[], parameters:{}), partitionKeys:[FieldSchema(name:ds, type:string, 
comment:null)], parameters:{transient_lastDdlTime=1264027720})
Time taken: 3.062 seconds
hive> describe extended zshao_ttp partition(ds='2010-01-01');
OK
d       string
ds      string

Detailed Partition Information  Partition(values:[2010-01-01], dbName:default, tableName:zshao_ttp, createTime:1264027788, 
lastAccessTime:0, sd:StorageDescriptor(cols:[FieldSchema(name:d, type:string, comment:null)], location:hdfs://hdfs:9000
/user/hive/zshao_ttp/ds=2010-01-01, inputFormat:org.apache.hadoop.mapred.SequenceFileInputFormat, 
outputFormat:org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat, compressed:false, numBuckets:-1, 
serdeInfo:SerDeInfo(name:null, serializationLib:org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, parameters:
{serialization.format=1}), bucketCols:[], sortCols:[], parameters:{}), parameters:{transient_lastDdlTime=1264027788})
Time taken: 0.436 seconds


hive> insert overwrite table zshao_ttp partition (ds='2010-01-01') select d from zshao_ttp where ds = '2010-01-01';
Total MapReduce jobs = 2
Launching Job 1 out of 2
Number of reduce tasks is set to 0 since there's no reduce operator
Starting Job = job_200912262300_1111, Tracking URL = http://jobtracker:50030/jobdetails.jsp?jobid=job_200912262300_1111
Kill Command = hadoop/bin/../bin/hadoop job  -Dmapred.job.tracker=jobtracker:50029 -kill job_200912262300_1111
2010-01-20 15:04:15,272 Stage-1 map = 0%,  reduce = 0%
2010-01-20 15:05:16,895 Stage-1 map = 0%,  reduce = 0%
2010-01-20 15:06:16,768 Stage-1 map = 100%,  reduce = 0%
2010-01-20 15:06:43,929 Stage-1 map = 100%,  reduce = 100%
Ended Job = job_200912262300_1111
Launching Job 2 out of 2
Moving data to: hdfs://hdfs:9000/tmp/hive-zshao/262641680/10000
Loading data to table zshao_ttp partition {ds=2010-01-01}
Moved to trash: /user/hive/zshao_ttp/ds=2010-01-01
2 Rows loaded to zshao_ttp
OK
Time taken: 187.049 seconds


hive> describe extended zshao_ttp partition(ds='2010-01-01');
OK
d       string
ds      string

Detailed Partition Information  Partition(values:[2010-01-01], dbName:default, tableName:zshao_ttp, createTime:0, 
lastAccessTime:0, sd:StorageDescriptor(cols:[FieldSchema(name:d, type:string, comment:null)], location:hdfs://hdfs:9000
/user/hive/zshao_ttp/ds=2010-01-01, inputFormat:org.apache.hadoop.mapred.SequenceFileInputFormat, 
outputFormat:org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat, compressed:false, numBuckets:-1, 
serdeInfo:SerDeInfo(name:null, serializationLib:org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, parameters:
{serialization.format=1}), bucketCols:[], sortCols:[], parameters:{}), parameters:
{lastQueryTime=1264028626290,archiveFlag=false,transient_lastDdlTime=1264028626})
Time taken: 0.283 seconds