> ...and it's really annoying if you need older software.

Bummer, and a real shame given how seemingly common regressions are in this space. Not my specialization, but anecdotally over a decade or so, I've encountered scenarios on MAX 7000 and Cyclone II (Quartus II v9.0 builds, v10.x breaks), Virtex-7 (Vivado v2018.3 builds, v2019.1 breaks) and Virtex-5 (ISE v14.6 builds, v14.7 breaks).