[Avodah] When Bittul Chometz precedes Mechiras Chometz

[Akiva Miller]

.
On Erev Pesach morning, we explicitly divest ourselves of ALL the
chometz we own, whether we know about it or not, with no exceptions.

It seems to me that there is indeed one very obvious exception,
namely, the chometz which the Rav has not yet sold to the non-Jew. (I
suppose that one could avoid this situation by delaying the bittul
until the very end of the fifth hour, but the danger of missing that
deadline scares me.)

I have not seen any sifrei halacha, nor any pamphlets or bulletins or
websites, that mention this point. Perhaps everyone just presumes that
people have this exception in mind when they say the bittul?

Here's a better way to phrase my question: Would a mental reservation
be valid in this case? Perhaps halacha ignores the mental reservation,
and only cares about the actual words of the bittul - which explicitly
refers to ALL the chometz. If halacha does allow this exception - and
people do have this exception in mind either explicitly or implicitly
- then there is no problem. But I would like to hear that this is
confirmed by the poskim.

Some might say, "What's the problem? There is chometz in his house,
but he got rid of it via BOTH bitul and mechira! He is surely okay!"

No, I can see two very serious problems. But before I go further, I
must reiterate that these problems would only arise in the case where
one does his Bitul Chometz BEFORE the Rav transfers ownership to the
non-Jew. (If the ownership transfer occurs first, then at the time of
the Bitul, there is no problem, because the only chometz still in his
possession is really and truly nothing more than the chometz that he
is unaware of.)

1) If there is still chometz in his home, and he is expecting for it
to be sold to a non-Jew several minutes or hours later, but the words
of the bittul - "All the chometz in my possession, whether I know
about it or not" - are to be taken a face value, doesn't this case
aspersion on the sincerity/validity of the bittul?

2) Perhaps even worse: After Pesach, when it is time to re-acquire the
chometz, he can no longer rely on "he got rid of it via BOTH bitul and
mechira! He is surely okay!" Rather, a determination must be made. If
he got rid of it via mechira (despite happening after the bittul),
then the chometz may be eaten. But if, in the final analysis, he got
rid of it via bitul, then it is assur b'hanaah (Mechaber 448:5, MB
448:25).

So... anyone know if any poskim write about this?

Akiva Miller