When the destination file cannot be copied in 32 bit installer of 64 bit dlls (going to system32) temporary file attempted at system32 (as that is the destination directory) currently ends up in syswow64. When wineboot is later processing PendingFileRenameOperations the redirection of the source file is not performed (and there is no way to guess that the file was redirected).
-- v2: msi: Disable FS redirection for temporary file in cabinet_copy_file().