Note that in the single edit, if you leave one of the estimate fields empty, it automatically assumes the value specified in the other field. For example, if you specify the Original Estimate to be 4h, and leave the Remaining Estimate field empty, then it will be automatically populated with the value of 4h. The values can be changed whenever needed. In bulk edit, this behavior is only there if you select to change both fields. This rule does not apply to the Legacy Mode, where you can only update the Original Estimate until you start logging work.