date -u vs. CST

[jidanni]

$ for i in E C M P; do for i in ${i}ST; do echo -n $i:; date -ud "7:00 $i"; 
done; done
EST:Wed Sep  3 12:00:00 UTC 2008
CST:Wed Sep  3 13:00:00 UTC 2008
MST:Wed Sep  3 14:00:00 UTC 2008
PST:Wed Sep  3 15:00:00 UTC 2008
$ for i in E C M P; do for i in ${i}ST; do echo -n $i:; date -d  "7:00 $i"; 
done; done
EST:Thu Sep  4 20:00:00 CST 2008
CST:Thu Sep  4 07:00:00 CST 2008 <-----UH OH
MST:Thu Sep  4 22:00:00 CST 2008
PST:Thu Sep  4 23:00:00 CST 2008

Why should the China zone kick in and out depending on -u? Note that I
object to it being interpreted differently in the input, not the
output.