This is a huge problem with the ruby client that has had an open bug about this: https://github.com/zendesk/zendesk_api_client_rb/issues/420
Safe_update *does not work* if you use the ZD api ruby client. This is a huge problem and causes collisions on tickets. This is not fixable by anyone but Zendesk. The source of the problem and a solution were laid out in the bug 2 years ago. This has been causing us issues for years now.
We've gotten a card created for this issue. In the interim, we've put together a workaround and added it to the issue in github.