Duplicate entry on insert into cache

Sometimes such error appears on my site:

user error: Duplicate entry 'locale:ru' for key 1
query: INSERT INTO deb_cache (cid, data, created, expire) VALUES('locale:ru', 'a:1220:{s:30:\"%sitename administration pages\";s:30:\"%sitename administration pages\";s:390:\"Welcome to the administration section. Below are the most recent system events. To get started please choose an item in the left column. If there is an arrow it will expand into a submenu. To jump up a level use the link,bread crumbs, above this block of text. To return to the home page click on the site name, and to go to Drupal\'s home page click on Druplicon, the drop on to the right.\";s:390:\"Welcome to the administration section. Below are the most recent system events. To get started please choose an item in the left column. If there is an arrow it will expand into a submenu. To jump up a level use the link,bread crumbs, above this block of text. To return to the home page click on the site name, and to go to Drupal\'s home page click on Druplicon, the dro in /home/axel/site/includes/database.mysql.inc on line 90.

I'm use last CVS version of Drupal. Anyone has comments about this error?