Why did some previous commits appear in the response for commits since a commit?

[Serhii Mormul]

I try to get merge commits since a specific commit. The commit data is

{"id":"000000000","displayId":"000000000","author":{"name":"user1","emailAddress":"user1@company.com","id":2657,"displayName":"User 1","active":true,"slug":"user1","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user1"}]}},"authorTimestamp":1609916981000,"committer":{"name":"user1","emailAddress":"user1@company.com","id":2657,"displayName":"User 1","active":true,"slug":"user1","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user1"}]}},"committerTimestamp":1609916981000,"message":"PROJ-3| remove login usage","parents":[{"id":"7777777777","displayId":"7777777777","author":{"name":"user_1","emailAddress":"user1@company.com"},"authorTimestamp":1609866893000,"committer":{"name":"user_1","emailAddress":"user1@company.com"},"committerTimestamp":1609866893000,"message":"PROJ-3| add missing space","parents":[{"id":"888888888888","displayId":"888888888888"}]}],"properties":{"jira-key":["PROJ-3"]}}

I use the request like

curl -D- -u user:password -X GET -H "Content-Type: application/json" https://stash.company.com/rest/api/1.0/projects/PROJ/repos/services/commits?merges=only\&since=000000000

 And received a result with two commits which happened BEFORE the specific commit

[{"id":"11111111111","displayId":"11111111111","author":{"name":"user3","emailAddress":"user3@company.com","id":1356,"displayName":"User 3","active":true,"slug":"user3","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user3"}]}},"authorTimestamp":1609933155000,"committer":{"name":"user3","emailAddress":"user3@company.com","id":1356,"displayName":"User 3","active":true,"slug":"user3","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user3"}]}},"committerTimestamp":1609933155000,"message":"Pull request #3323: merge PR 3323 message.","parents":[{"id":"2222222222","displayId":"2222222222"},{"id":"33333333333","displayId":"33333333333"}],"properties":{"jira-key":["PROJ-3"]}},
{"id":"33333333333","displayId":"33333333333","author":{"name":"user1","emailAddress":"user1@company.com","id":2657,"displayName":"User 1","active":true,"slug":"user1","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user1"}]}},"authorTimestamp":1609917535000,"committer":{"name":"user1","emailAddress":"user1@company.com","id":2657,"displayName":"User 1","active":true,"slug":"user1","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user1"}]}},"committerTimestamp":1609917535000,"message":"Merge branch 'PROJ-3-p2' of https://stash.company.com/scm/project/service into PROJ-3-p2","parents":[{"id":"000000000","displayId":"000000000"},{"id":"66666666666","displayId":"66666666666"}],"properties":{"jira-key":["PROJ-3"]}},

{"id":"2222222222","displayId":"2222222222","author":{"name":"user2","emailAddress":"user2@company.com","id":25,"displayName":"User 2","active":true,"slug":"user2","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user2"}]}},"authorTimestamp":1609874064000,"committer":{"name":"user2","emailAddress":"user2@company.com","id":25,"displayName":"User 2","active":true,"slug":"user2","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user2"}]}},"committerTimestamp":1609874064000,"message":"Pull request #3321: merge PR 3321 message.","parents":[{"id":"4444444444","displayId":"4444444444"},{"id":"55555555555","displayId":"55555555555"}],"properties":{"jira-key":["PROJ-2"]}},
{"id":"4444444444","displayId":"4444444444","author":{"name":"user2","emailAddress":"user2@company.com","id":25,"displayName":"User 2","active":true,"slug":"user2","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user2"}]}},"authorTimestamp":1609871700000,"committer":{"name":"user2","emailAddress":"user2@company.com","id":25,"displayName":"User 2","active":true,"slug":"user2","type":"NORMAL","links":{"self":[{"href":"https://stash.company.com/users/user2"}]}},"committerTimestamp":1609871700000,"message":"Pull request #3322: merge PR 3322 message.","parents":[{"id":"99999999999","displayId":"99999999999"},{"id":"10101010101","displayId":"10101010101"}],"properties":{"jira-key":["PROJ-3"]}}]

My only question is why?