How is supposed to be protected the units list?

[Matthew Jacob]

That's a fair comment. There is at least one case where this additional 
lock has helped. It probably needs rethinking a little later, but for 
now it does seem to help people.
> I have already told my opinion, that second lock may be not needed. I
> would like to think a bit more about both patches after getting back
> from the conference. Thanks,
>
>