In a Bionic Merge Task (in an Advanced Outreach, but I imagine it would work the same for a Rule), I'm using an email address as the "Merge On" field between two data sets. Is that join going to be case-sensitive? It isn't indicated in the documentation.
We are introducing ToUpperCase() and ToLowerCase() formula functions in the transformation task of Bionic Rules for fall release. This will help in resolving any case sensitive field comparisons including merges/joins.