JSON-RPC: "Internal error" on subscribe_cdboper method, if tailf:display-when statement present in parent container

The minimal YANG module:

module test {
  namespace "http://example.com/test/test";
  prefix test;
  import tailf-common { prefix tailf; }
  container test {
    leaf enabled { type boolean; default 'true'; }
    container dynamicDisplay {
      tailf:display-when "../enabled = 'true'";
      container oprational{
        config false;
        leaf value1 { type int32; }
        leaf value2 { type int32; }

JSON-RPC will return ‘rpc.internal_error’ if you try to use subscribe_cdboper:

No problems if I remove ‘tailf:display-when’ statement or replace it with ‘when’ statement.

I tried different versions of CONFD and found that the error exists starting from confd-6.1.2 and to at least confd-6.3 (I don’t have versions after 6.3). No problems for confd-6.1.1 and earlier (tried up to 5.3.7).

Seems like that issue was discovered and fixed in ConfD 6.5 released in October 2017.