Event Summary report instances break on upgrade due to changed event ID storage format

I encountered this error while upgrading a site from 4.3.6 to 4.6.2. I'm not sure in what version CiviCRM version the report was originally instantiated, but I think any pre-4.5 instances will fail similarly due to the introduction of the select2 and/or entityRef widgets.

Loading the form results in this error:

Database Error Code: Unknown column 'Array' in 'where clause', 1054
Additional Details:
Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -19
[message] => DB Error: no such field
[mode] => 16
[debug_info] =>
SELECT civicrm_participant.event_id AS event_id,
civicrm_participant.status_id AS statusId,
COUNT( civicrm_participant.id ) AS participant,
SUM( civicrm_participant.fee_amount ) AS amount,
civicrm_participant.fee_currency

FROM civicrm_participant

WHERE civicrm_participant.is_test = 0
AND civicrm_participant.event_id IN ( Array )

GROUP BY civicrm_participant.event_id,
civicrm_participant.status_id

The problem is that, between versions, CiviCRM changed how the event_type_id_value is stored in civicrm_report_instance.form_values. The (unserialized) pre-upgrade record looks like this:

[id_op] => in
[id_value] => Array
(
[0] => 25,
[1] => 26,
)

... while the same report instance, built post-upgrade, looks like this (unserialized)...

[id_op] => in
[id_value] => 25,26