Oh, thanks. Now, I understand correctly. The internal MM DB searching wasn't all right. As you wrote '[', ']', '_' have't found.
It is fixed in B4
Thank you.

There's a similar issue searching for underscore character "_"

Thank you for your reply Ludek.

I think I was not clear enough in my posting. I don't want to change anything in the way Amazon saves info about albums. I only noticed that Amazon saves a lot of titles like
Songtitle 1 [rare]
Songtitle 2 [#]
Songtitle 3 [Live]

I don't like that kind of information in the title field because strictly it doesn't belong there. There are others fields to save that kind of information.
What I usually did was searching for square brackets in the title field. Then I manually erased most of the information between the [ and the ].
This worked perfectly in MM 2.5, but in MM 3 it is no longer possible to search for square brackets. Fortunately I can still search for round brackets with the search function of MM3. To find all square bracket I should have to walk through my database manually.
I hope this can be fixed in B4 or later.

It works the same way as in MM 2.5, the string '[' is posted to amazon and the results are retrieved from amazon. I cannot see what we could do about this

In beta 3 I still can't search for strings like [ and that is pitty because square brackets are often used on the Amazon site to distinguise certain info in track titles.
Searching for round brackets works perfectly.