Timestamp shift when importing data

I am trying to migrate several years of historical data with timestamps
from an MS Access database to Postgres. I am running into an issue where
specific dates/times get pushed one hour ahead, which creates duplicate
date/time stamps or failes the import if I have that defined as my
primary key. The time that gets shifted is always 2:00 AM to 2:55 AM
(data is in 5 minute blocks). What I don't understand is that it only
seems to happen on the following dates (m/d/yy format):

4/7/02
4/6/03
4/4/04
4/3/05
4/2/06

For example, on these days, 4/7/02 2:00 AM imports to 4/7/02 3:00 AM.
4/6/03 2:15 AM imports as 4/6/03 3:15 AM, etc. All other dates and times
do not give any errors. I have tried to extract the date and create a
text field in MS Access, I get the same error when imported to Postgres.
Is there some significance to these dates?

Thanks,
Peter Jolles