Slack import fails in Mattermost 1.3?

Hi all-

I just tried importing from Slack and got some strange results: channels were created, but no users were created, and no posts were added (I'm guessing that's a side effect of no users?). I did this on our production server, but on a new test team. I created the team, and in the System Console my account was labeled Team Admin. The server logs have a lot of these messages, but nothing related to account creation:

[2016/01/06 13:38:03 EST] [WARN] Unsupported post type: message, channel_join
[2016/01/06 13:38:03 EST] [WARN] Slack bot posts are not imported yet

Oh, could the failure to create accounts be related to Mattermost's "Enable User Creation" setting? I turned that off when setting up the production server, figuring I would send invites to team members...

For the record, I'm running Mattermost 1.3.0 build 4896.

Thanks!