upgrade to 2.9.2 No date updates on wp_blog_versions

Hi,
I ran a site-wide upgrade from 2.8.6 to 2.9.2 wpmu.
In the wp_blog_versions table the db_version field correctly changed to 12329 but the last_updated field kept its old value.
Is this a normal behavour, a bug or have I made something wrong?

I haven’t noticed yet any problems in my blogs with my 2.9.2.

Thanks in advance
Lena Stergatu