I just ran Windows Update on a new Windows 2008 Standard Edition SP2 64-bit server today. Since then Windows Explorer keeps opening folders in new windows when I double click on them.
I've double check that the folder options are correct:
Organize -> Folder and Search Options -> Browse folders -> Open each folder in the same window - this is selected.
I've googled around and there was suggestion that changing the following registry keys
Default value should work:
%SystemRoot%\Explorer.exe /same,/e,/idlist,%I,%L or
I've even rebooted the machine and tried different accounts but the behaviour remains the same.
I've inspected each update but nothing jumps out as being a change to the behaviour of Explorer.