Slack import fails in Mattermost 1.3?

In a stock a development environment I checked out the release-1.3 branch, did a test import, and the behavior is the same as my production system (no users created, channels created, no posts added).

I do see a few more messages in my terminal:

[01/12/16 7:57:04] [DEBG] /api/v1/teams/import_team
[01/12/16 7:57:10] [WARN] Unsupported post type: message, channel_join
[01/12/16 7:57:10] [DEBG] User: U08K1GKRA does not exist!
[01/12/16 7:57:10] [DEBG] User: U08K2HWAC does not exist!

The "user does not exist" line occur a lot, possibly for every message?

I can probably remove most of the channels while leaving some of the off-topic discussions, but I'd still rather not post team members' emails to the public internet. Is there a way to share the modified file with a small group of Mattermost developers?

Thanks!