I am on v1.8.0, I have no experience with older versions.
This trivial program results in a cln::notreached_exception being thrown.

#include <ginac/ginac.h>
int main() {
  GiNaC::ex a = GiNaC::Pi;
  GiNaC::ex b = 1;
  std::cout << GiNaC::ex_to<GiNaC::numeric>(a+b).to_double() << std::endl;
  return 0;
}

Compiled with:

g++ test.cpp -lginac -lcln

Here is the full exception message:

what():  Internal error: statement in file real/conv/cl_R_to_double.cc, line 48 has been reached!!
Please send the authors of the program a description how you produced this error!

I would expect that to work, am I wrong?