Are you invoking the HTTP request multiple times with the same data, or do you mean you do it once and then they show up multiple times in the CLI commands? It may be the same core problem as a known issue[1] if you only do it once.
It doesn’t matter how many times I invoke request. Result is always the same. What is more interesting, when I restart Asterisk by ‘core restart now’ then duplicate entry disappears and only one is printed by CLI command. Then every new HTTP PUT with the same data provided rewrite existing entry. Deleting entry and creating it again prints duplicates. Seems like restarting Asterisk is fixing the issue but that is not a correct solution.
You can file an issue on the issue tracker[1] with an ARI script and configuration to reproduce, but I have no timeframe on when it will be looked into.