Download and unpack the new 5.0 version, e.g. from http://dev-builds.libreoffice.org/pre-releases/win/x86/nomergelibs/ Look into the file bootstrap.ini. Notice the line UserInstallation=$SYSUSERCONFIG/LibreOfficeDev/4 That means, that folder "user" from the old directory is used. That should not happen for a major release.
Christian: thought you might be interested in this one since http://cgit.freedesktop.org/libreoffice/core/commit/?id=468aaa1bcf96c86c4a33b5dcd0aabb41e14b042d seems to show that having a profile with version 4 is on purpose.
Julien: it was decided in an ESC meeting that the profile will be kept at 4. http://listarchives.libreoffice.org/global/projects/msg01651.html
*** Bug 93057 has been marked as a duplicate of this bug. ***
Badfully... but I suppose good technical reasons justify this (didn't find them reading http://listarchives.libreoffice.org/global/projects/msg01651.html)
*** This bug has been marked as a duplicate of bug 93057 ***