Microsoft has released a fixed build

Dallas A But you didn't try with that new version, do you?

I couldn't fix it so far in the driver. I've got to the point where I could not understand why doesn't it work. Maybe indeed there is/was some issue in the Access itself, but I don't really hope for that. MySQL driver has the same problem, though.

Btw, I see the problem only when key field contains non-ascii caharacters. Otherwise works fine for me. Could you confirm you have it the same way?

Yes, I confirm that it was any non-integer key. I'm using utf8mb4 charset. I needed to for some reason.

Dallas A Could you pleased check if your Access is 32b or 64b?

We have all switched to 64b in my company.

In 32b is the same problem.

Unfortunately it won't make into the coming release, as we don't have the solution yet. As I said, but maybe was not very clear - I understand where the problem is. But fixing got me to the point, that situation with varchar keys got even worse, while everything in the odbc trace or while tracing the execution, looks to be correct.
Since this issue in the connector was like since forever, and there is workaround - e.g. adding auto_increment primary key, and adding unique constraint on the varchar field instead of primary key, but that unique key name is greater than PRIMARY - then Access will pick PRIMARY key for use as row identifier, I've downgraded the bug to critical.