Unable to schedule activities for leads

I assume this is a known issue, but I don't see anything in the feed below. 

I just started testing Leads Inbox last Friday. So far, I am unable to schedule an activity for a lead using the "Schedule an activity" link. I was able to create an activity using the shortcut buttons (1h, 3h, tomorrow), but I cannot edit the activity once it's created. 

This seems like a critical issue unless I'm doing something incorrect. I'm sorry if this is reported and resolved elsewhere.