Sitecore Support has determined that this is a bug, public reference number 221523.
At this timeWhile previously it appears thatwas necessary to contactingcontact Sitecore Support if you runran into this issue is the resolution, as there's a new SitecoreSitecore's Knowledge Base has an article covering this issue, with the necessary hotfix.Kernel
This issue is resolved in 9.dll that can be provided to fix this1.