They uncovered one bug: in edit/003-shortcuts.mu <scroll-down> was returning 0 for an address in one place where I thought it was returning 0 for a boolean. Now we've eliminated this bad interaction between tangling and punning literals.
Hypothesis: this is needed to build McCarthy's amb operator. https://rosettacode.org/wiki/Amb
All the bugfixes since commit 4135 have been aimed at getting this example program work.
Kartik Agaram