CockroachDB C++ transaction retry issue

Question

I'm trying to run the basic C++ example, basically:

void executeTx(
    pqxx::connection *c, function<void (pqxx::dbtransaction *tx)> fn) {
  pqxx::work tx(*c);
  while (true) {
    try {
      pqxx::subtransaction s(tx, "cockroach_restart");
      fn(&s);
      s.commit();
      break;
    } catch (const pqxx::pqxx_exception& e) {
      // Swallow "transaction restart" errors; the transaction will be retried.
      // Unfortunately libpqxx doesn't give us access to the error code, so we
      // do string matching to identify retryable errors.
      if (string(e.base().what()).find("restart transaction:") == string::npos) {
        throw;
      }
    }
  }
  tx.commit();
}

However, transactions never get retried correctly, I'm getting this error:

current transaction is aborted, commands ignored until end of transaction block

Looks like the top level transaction pqxx::work tx(*c); gets poisoned? The second iteration of the loop always fails