the only other reference to this error i've been able to find is here:
http://comox.textdrive.com/pipermail/wp-testers/2008-March/007606.html
the fact that this reporter is describing a "2.5 RC2 to 2.5 RC3" upgrade makes me think, like MichaelH mentioned above, that somehow the current version is being reported incorrectly before the upgrade.
looking at the upgrade script, it checks the db_version at line 26. looking at the options table, my db_version has a value of 7558, while the 2.5 tag in subversion is at revision 7567...
so the upgrade script is likely trying to upgrade from a pre-2.5 version, when in reality the db is already at 2.5. meaning, i think i can ignore this error... can anyone give me a sanity check here? specifically, how to be 100% sure (via phpmyadmin or CLI compared to the Database Description MichaelH linked above), that the db schema is as it should be.
looking at the comments table, i see:
Keyname Type Cardinality Action Field
comment_approved INDEX 1 Edit Drop comment_approved 1
looking at the posts table, i see:
Keyname Type Cardinality Action Field
PRIMARY PRIMARY 59 Edit Drop ID
type_status_date INDEX 59 Edit Drop post_type
post_status 1
post_date
ID