Cannot use table cell input in LibreOffice Writer.

I inserted a 20: 2 vertical / horizontal table in LibreOffice Writer. And the height of the line was set to 15. I entered the characters in one of the tables. Then, for some reason, the same character appears in other tables. How can I solve it?
By the way, the latest version is used.

What is latest? There are at least 2 latest versions - one for still and one for fresh. And your description is quite confusing. You add 1 (!!!) table, enter characters in one of the tables (plural, so there are all of a sudden more of 'em) and characters appear in other tables as well (though you created one table only).