After compiling and installing the latest FLDIGI I found a bug - if the radio dial is moved while FLDIGI is running (with RigCAT control operating normally) I found FLDIGI crashes. This has never happened in previous versions. Fldigi should just track the changing rig VFO frequency, not crash!
I ran make uninstall and removed it and simply reinstalled the Debian packaged version 4.1.18, which runs perfectly well enough, without the new esoteric modes available in 4.2.03