Update to this, it's been sent to the R&D group via a support case.  Apparently they're able to reproduce this issue in both W18 and Summer 17 orgs, however I had this working in Summer 17 - and the switch to W18 broke the functionality.  Since they're saying it's not a regression issue, it's taking a lower priority.

For anyone at Salesforce looking at this, my case # is 17249103

I'm waiting to see if they're going to make a Known Issue of it for tracking.

Edit:  This was fixed in a patch release.