When opening InDesign documents (.indd) InDesign/InCopy create an InDesign Lock file (.idlk) that other instances of InDesign/InCopy check for to determine if the file is in use. If the file is in use, other instances of InDesign/InCopy are designed to alert the user that the document is in use by another user, and not allow it to open. When this is done in InDesign CS5 versions 7.0 and 7.0.1 (Swedish/German only versions), the user gets no alert, however, the document is opened in a read-only mode which makes it impossible for anyone but the first user to open the file able to save it to that same name and location.
A similar function exists when checking out a linked InCopy story from within an InCopy assignment (.icma) or layout (.indd). Subsequent users should be alerted that the content is currently be edited by another user. Instead, subsequent users can open the same document or check-out the same assignment without receiving any warning. This leads to a state where multiple users can edit the contents, and only the changes from the last user to save the document are preserved.
This primarily applies when users are opening the files from both a Windows and a Mac OS system. However, some users have also reported experiencing the problem when all clients on are Mac OS, bu the files are stored on some types of non-Mac OS file servers.