Strange (missing)? history in DIM pool

[miesi]

(see ITOUDP-2587)
we observed that within the pool PraesenzNetz-26 we have ~120 free IP addresses:

$ ndcli list pool PraesenzNetz-26
prio subnet           gateway free total
   1 82.165.188.64/26           61    64
   2 212.227.109.0/26           62    64
INFO - Total free IPs: 123

However if you check the history, you can see that all IPs (out of 82.165.188.64/26) should be allocated:

$ ndcli history pool PraesenzNetz-26
timestamp                  user         tool   originating_ip objclass name            action
2019-11-18 12:03:43.589579 mfleischmann native 10.22.0.11     ippool   PraesenzNetz-26 create subnet 212.227.109.0/26
2019-11-18 09:06:02.638080 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.65
2019-11-16 05:30:02.957326 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.126
2019-11-16 05:27:02.961421 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.125
2019-11-16 05:24:02.950202 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.124
2019-11-16 05:21:03.257942 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.123
2019-11-16 05:18:03.485246 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.122
2019-11-16 05:15:02.678831 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.121
2019-11-16 05:12:03.025745 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.120
2019-11-16 05:09:02.655382 sanetdotmw   native 10.46.135.26   ippool   PraesenzNetz-26 create static 82.165.188.119

And none of these IPs have been freed again.

Could you please check why that info is missing here?

todo: create testcase and validate that this is not happening in the current codebase.