Why the data changes it's value by itself!

Hello,

We been having a problem lately with some data changing their value without modifying them.
We used to backups to see the difference:
this was the first backup
INSERT INTO journal VALUES(28382,698,754,7116,7,0.01,'20060606','15415773',1,3,4,1,1,5,77,1,17,2,1,1,15,1,1,2,0,32252,0,14183,0,0,0,'A1',0,0);
INSERT INTO journal VALUES(28383,698,3201,26018,7,21.74,'20060606','15415773',1,3,4,1,1,7,175,1,33,2,1,1,15,1,1,1,0,71451,1,14183,0,0,0,'P1',0,0);
INSERT INTO journal VALUES(28384,698,3201,26018,9,1.52,'20060606','15415773',1,3,4,1,1,7,175,1,33,2,1,1,15,1,1,1,0,71451,0,14183,0,0,0,'T11',0,0);
INSERT INTO journal VALUES(28385,698,3201,26018,10,1.74,'20060606','15415773',1,3,4,1,1,7,175,1,33,2,1,1,15,1,1,1,0,71451,0,14183,0,0,0,'T12',0,0);

and the second backup

INSERT INTO jnlsale VALUES(28382,698,754,7116,7,0.01,'2000606','1541577',1,3,4,1,1,5,77,1,17,2,1,1,15,1,1,2,0,32252,0,14183,0,0,0,'A1',0,0);
INSERT INTO jnlsale VALUES(28383,698,3201,26018,7,1.20932764209866e-307,'20060606','15415773',1,3,4,1,1,7,175,1,33,2,1,1,15,1,1,1,0,71451,1,14183,0,0,0,'P1',0,0);
INSERT INTO jnlsale VALUES(28384,698,3201,26018,9,1.52,'2000606','1541577',1,3,4,1,1,7,175,1,33,2,1,1,15,1,1,1,0,71451,0,14183,0,0,0,'T11',0,0);
INSERT INTO jnlsale VALUES(28385,698,3201,26018,10,1.29775128722884e-154,'20060606','15415773',1,3,4,1,1,7,175,1,33,2,1,1,15,1,1,1,0,71451,0,14183,0,0,0,'T12',0,0);

The values that change are: '20060606' to '2000606'
21.74 to 1.20932764209866e-307
etc

Thanks in advance,

Version used PostgreSQl 8.1.1 on Windows box with Windows 2000 server