Update Query doesn't affect all records

Hi!

I've got this update query:

http://pastebin.com/m2e29990

Can anyone tell me, how this is possible? If we insert 12 on the end, then
it decreases, but 11 remains the same. The problem only occurs, when the
where condition contains "sorrend > 9" or less.

It occured using "PostgreSQL 8.3.3, compiled by Visual C++ build 1400" and
"PostgreSQL 8.3.7 on i486-pc-linux-gnu, compiled by GCC gcc-4.3.real (Debian
4.3.2-1.1) 4.3.2" too.

Thanks,
Andor