there are differences in compiling via (1) Build_Isac.thy and via (2) ROOT.ML:
# (1) still accepts ref, while (2) requires Unsynchronized.ref
# (2) is more rigid in type checking (eg. "can't find a fixed record type")
1 This directory contains some administrative tools for the Isabelle
2 repository at TUM. They do not appear in proper distributions.