WPT lost untracked files in tools

Hi,

>From last week, we all meet an issue when fetch code for w3c/web-platform-tests to our old forked repository:

$ git fetch upstream
$ git merge upstream/master
Updating cdd6c0f..ffeb316
error: Updating the following directories would lose untracked files in it:
                tools
Aborting

But this issue is not met in new forked repository, I notice that we have changed the tools  as a sub module.
Don't I get correct way to fetch the changes, or is it an issue occurs by the changes?

Looking forward to your reply.


Thanks and BRs,
Li Hao