This bug is causing me a lot of problems but seems impossible to workarround it. Apparently it just happens with the version 6.9 and with a particular date "2008-03-08 23:59:59", not another.
Look!
Code:
carlosnblnx:/home/carlos # date --date='+1 seconds 2008-03-08 23:59:59' '+%F %H:%M:%S'
2008-03-08 23:00:00
Should be 2008-03-09 00:00:00!!!

Now with the same month and day but another year
Code:
carlosnblnx:/home/carlos # date --date='+1 seconds 2007-03-08 23:59:59' '+%F %H:%M:%S'
2007-03-09 00:00:00
Works!
Finally, same year, day.
Code:
carlosnblnx:/home/carlos # date --date='+1 seconds 2008-04-08 23:59:59' '+%F %H:%M:%S'
2008-04-09 00:00:00
I really don't know why this happens.

date version
Code:
carlosnblnx:/srv/www/htdocs/show_stat # date --version
date (GNU coreutils) 6.9
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software.  You may redistribute copies of it under the terms of
the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.

Written by David MacKenzie.