Table dublicates values

Hi all,

I am using postgresql on Glassfish server. When I restart the server for some reason, one of my databases' tables duplicates the values. For example aTable is from aDatabase:

select * from aTable
 col1                | col2
-----------------------+---------
 text/html         |    1672
 text/javascript |     374
 text/css          |      94
 text/xml          |      21
 text/plain        |      14
 text/html         |    1672
 text/javascript |     374
 text/css          |      94
 text/xml          |      21
 text/plain         |      14

Do you have any opinion why this is happening? I can write a workaround code to handle this situtation but I want to learn the reason for this. If someone has any opinion about this issue it will be highly appreciated. Thanks in advance.