Drupal 6 search incorrectly give error

I have drupal 6 installed on linux with mysql 5.6 and php 5.4. All working. 
But search give error: You must include at least one positive keyword with at least 3 characters. . I enter word with 5-6 characters. 

I try see logs of server and php, errors: 0. In admin panel: admin/settings/search all indexed on 100%. What this can be? I think, that drupal incorrectly checks for counting characters in search. May be need a module php? But I have installed all modules..

In database I have all tables on InnoDB.

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/20/feed