If you have a Post Function in your workflow that sets the remaining estimate to zero, and have a post function that will clear the remaining estimate to zero, it will change the original estimate to zero too.
Steps to reproduce:
1. Switch to Legacy Time Tracking Mode
2. Add a Post Function to your projects workflow that will set just the remaining estimate to 0m, not the original estimate.
3. Create a new issue with an Original Estimate of 5h
4. Close the issue and log 1 hour of work on the close screen, automatically adjust remaining estimate.
5. It will now have an original estimate of 0m and a remaining estimate of 0m, when the Original Estimate should remain at 5h.
This will not occur if you Create the issue, log work, then as a separate step, close the issue.