When minimizing tree-based diff, via `--minimization` switch only, Repair is Found, but get "Fatal error: exception Not_found"

[pdreiter]

After successfully repairing a program, consecutive run of GenProg with --minimization switch causes an Abort condition: "Fatal Error: exception Not_found"

I was able to duplicate the failure locally with a small set of configuration-default input.
The following configuration-default repairs successfully:

--seed <some number>
--program <my program>
--pos-tests <num pos>
--neg-tests <num neg>
--search ga
--popsize 500
--generations 10
--test-script ./my_test_script.sh

Add --minimization to this configuration-default, we see the following Abort occur:

search: initial population (sizeof one variant = 0.355664 MB)
	 16 original
	  0 s(32,36)
	  0 a(29,36)
	 16 a(32,14)
	 16 d(23)
	 14 s(13,11)
	 34 d(30)
	  2 d(32)
	 34 d(30)
	 34 d(30)
	 16 a(38,21)
	  0 a(10,28)
	 16 a(35,29)
	 16 d(23)
	 48 d(11)

Repair Found: d(11)
Repair Name: d(11)
Test Cases Skipped: ""
Current Time: 1566851558.149498
cilRep: shared size: 0.155056 MB
cilRep: private size: 0.29117 MB
/home/bss-lab-1/GenProg/genprog-code-master/src/repair.byte aborting: Not_found
Rep: saving test cache

Variant Test Case Queries: 270
"Test Suite Evaluations": 15

Compile Failures: 0
Wall-Clock Seconds Elapsed: 2.59036
  Activity Name                     Count Seconds = Percent of Total Time
  test_cache hit                      270   0.001 = 0.04266%
  rebuild files                       394   0.063 = 3.62924%
  compile                               8   0.429 = 24.5461%
  test                                131   1.254 = 71.782%
  TOTAL                                     1.747 = 67.0875% (avg CPU usage)
Fatal error: exception Not_found

[pdreiter]

the Abort condition occurs at
minimization.ml @ 162 let m = Cdiff.mapping node_map t1 t2 in