Migrate confusion - 0 ignored, 0 failed, but still unimported content is left

I'm upgrading from 7.x-1.5 to 7.x-2.3 and have followed directions here, but the results are confusing.

No errors appear, but I still have unimported records in OgMigrateMembership. I tried rolling back and re-running but I get the same results. The message after "Rollback and Import" is as follows:

Rolled back 1143 in 3.4 sec (19900/min) - done with 'OgMigrateMembership'
Processed 1143 (0 created, 1143 updated, 0 failed, 0 ignored) in 22.5 sec (3052/min) - done with 'OgMigrateMembership'

I can't easily display the table but here's the results:

Status	Migration		Total rows	Imported	Unimported	Messages	Throughput	Last imported
Idle	OgMigrateMembership	1425		1143		282		0		3052/min	2013-09-30 10:31:17
Idle	OgMigrateRoles		0		0		0		0		Unknown	2013-09-30 10:24:44
Idle	OgMigrateUserRoles	41		41		0		0		6089/min	2013-09-30 10:24:45

So do I do anything about those 282 Unimported Membership records? How can I determine what those are even? Is there a logging utility for Migrate?

Thanks for the help.