The Official SBS Blog : Files in Companyweb are Opening Read-Only After SBS 2008 UR2:
The Official SBS Blog : Files in Companyweb are Opening Read-Only After SBS 2008 UR2:
http://blogs.technet.com/sbs/archive/2009/05/07/files-in-companyweb-are-opening-read-only-after-sbs-2008-ur2.aspx

This is a wincer for me. Because I tested this before it was released on test boxes and I personally missed this. Testing isn't easy.
Read the complete post at http://msmvps.com/blogs/bradley/archive/2009/05/07/the-official-sbs-blog-files-in-companyweb-are-opening-read-only-after-sbs-2008-ur2.aspx