After increasing log.retention.hours from the default of 168 to 744 (31 days) I noticed that logs were being deleted at every cleanup interval.
scala> val retentionMs: Long = 60 * 60 * 1000 * 31 * 24
retentionMs: Long = -1616567296
This only appears to affect trunk. I'll attach the minor patch I'm using locally. Thanks.