Filtering on frequency_unit Breaks Recur report

On the Recurring Contributions report, selecting Frequency Unit as a filter throws a fatal error of "DB Error: Unknown Field". To reproduce on the demo instance:

1. Load the report at http://dmaster.demo.civicrm.org/civicrm/report/instance/21?reset=1&output=criteria
2. From the filters tab, select any option for frequency_unit i.e. "Frequency Unit is one of week, month"
3. Update Report
4. Export to CSV

The error thrown indicates that month and week are unknown columns. Probably caused by Recur.php using INT for frequency_units when the option was changed to a string in 4.5.