Developers on Launchpad denied to acknowledge the bug, even though it was reported widely on the internet.
The issue seems to have something to do with the way, OpenOffice authenticates with Samba. In order to get a different behaviour, one can change the way, OpenOffice is called.
If you start OOo from the menu, the call is:
ooffice -writer %U (with calc and the others following the pattern)This tells OpenOffice, it should hand the user credentials to samba and authenticate. The result is the well documented error, the file cannot be read or written, a dialog asking for username and password for workgroup MSHOME, etc. appearing.
Under Ubuntu 8.10 you can adjust the menu setting to:
ooffice-writer %F (same with all the others)If you have a connection to the Samba server (e.g. a share mounted), you can access the files there, both read and write.
This is a workaround for Ubuntu 8.10 (sorry for posting it so late, but I did not find out until recently).
Under Ubuntu 9.04 (bound to be out April 23, 2009) OpenOffice works with the %U parameter as well.