Why updating a ticket status to Solved also change assignee and group?

Hello, I'm updating a ticket with body

{
"ticket": {
"status": "solved",
}
}

This update is done with an API user called TK.

The problem I have is that the status is update correctly but assignee_id and group_id are also updated to be equal to the user TK. I do not want to update the assignee_id or the group_id.

The ticket event history shows that all these 3 fields have been updated, but the REST call body only contained the new status.

Thanks