On a number of non-PC systems using uClibc 0.9.28, I have observed that the daylight saving change did not occur at 25 March 2012 01:00, timezone was still GMT.

Experimenting with setting various dates, it seems that while the timezone setting seems correct, the change would only occur in April. Observe:

# cat /etc/TZ
GMT0BST-1,M3.5.0/02:00,M10.5.0/02:00
# date -d 032412002012
Sat Mar 24 12:00:00 GMT 2012
# date -d 032512002012
Sun Mar 25 12:00:00 GMT 2012
...
# date -d 033112002012
Sat Mar 31 12:00:00 GMT 2012
# date -d 040112002012
Sun Apr  1 12:00:00 BST 2012

The change back seems to work:

# date -d 102712002012
Sat Oct 27 12:00:00 BST 2012
# date -d 102812002012
Sun Oct 28 12:00:00 GMT 2012

Last year was fine:

# date -d 032612002011
Sat Mar 26 12:00:00 GMT 2011
# date -d 032712002011
Sun Mar 27 12:00:00 BST 2011

Next year seems fine as well:

# date -d 033012002013 
Sat Mar 30 12:00:00 GMT 2013
# date -d 033112002013
Sun Mar 31 12:00:00 BST 2013

Adjusting the TZ will solve the problem:

# cat /etc/TZ
GMT0BST-1,M3.4.0/02:00,M10.5.0/02:00
# date -d 032412002012
Sat Mar 24 12:00:00 GMT 2012
# date -d 032512002012
Sun Mar 25 12:00:00 BST 2012

This seems to indicate that there is a difference between the 4th and last week, even though 5, meaning the last given day of the month, should do the right thing anyway, more so as any 25th day is the last of that day in any month.