Non-sql plain text search in console currently works by merely hiding the real where clause from your eyes. Effectively when you plain-text-search for a string line ‘mystring’ the request sent is
yourcolumn1 like '%mystring%' or yourcolumn2 like '%mystring%' or yourcolumn3 like '%mystring%' or ...
So if your table has lots of columns, it is quite possible that this hidden query grows up to more than 2048 characters.