Greets.
The second point below might be a configuration issue, but I will put it in here anyhow. The first point is definitely a bug.
1) There is a mis-typed parameter symbol in line 46 of the MySQLStore.php file. There is a "!" where it should be a "?" (at least, with it being a !, there was a problem parsing for a prepared statement).
2) Transactions do not seem to be implemented well for SQLStore in general. In my (brief and non-comprehensive) testing, it seemed that Auth_OpenID_DatabaseConnection::commit() was called without Auth_OpenID_DatabaseConnection::begin ever having been previously called (so it was trying to commit a non-existant transaction and therefore failing).