When the assigned work is greater than the real work but the activity is actually done

What is the advised way to handle the following case?

- An activity was planned with Assigned work: 8 h to Resource A.
- This assigned work was found by Resource A (while performing the activity) to be exaggerating the required effort which is actually 1 h.
- Resource A reported the 1 h as real work and the activity was marked by the Project Leader as done
- Now, the activity cannot be removed from the Real work allocation screen as there is still left work of 7 h.
- The activity also cannot be closed due the error Invalid controls. Unable to close an element with left work.
- The Project Leader set the validated work to 1 hr.
- The activity still cannot be closed due to the same error in addition to the indicator reassessed work compared to validated work

Is their a way to keep the information that the planned assigned work was incorrect and that the real work was enough to mark the activity as completed?
We faced this case several times. The easy way is to make the assigned work itself equal 1 h (so there is no more left work required). However, this would hide the fact that the planned assigned work was not accurate and does not give us the opportunity to enhance the accuracy of the estimation of the workloads and hence the accuracy of planning.

Hmmm.
You made me notice that left work is editable by both the resource and the project lead. I have not tried to edit left work previously and didn't even notice that it is an editable text field I thought it is always calculated from assigned - real.
I think this should somehow be clarified a bit more in the manual or the UI.
Thanks for the advice

In the UI, the field is clearly editable. I don't know how to point this out more : have it blink ?

Probably. It would be cool .

Based on your description, the left work field has a unique behavior. It is by default calculated from assigned - real but the calculation result can be overriden by an ad-hoc value. My understanding is that it does not reset to default "calculated from assigned - real" behavior again if it is once overriden (Am I right? ) Also, it is not editable when the activity is in status done but editable before this status and if the activity is re-opened. (Are there other such unique behavior fields in the UI?) Either way, if the field is unusual like this, it should be stressed on the UI by something like a different border color, a different background color, a bold text, a different text color (especilly if it became no longer calculated and the value is merely an input value) or a mix of these .

In the manual, I think an example or describing the use case and the behavior would make it clearer to the reader.
Left work is rarely entered in estimation step as the project manager knows only the needed workload and enters it in the assigned field. (Unless you are referring to an activity that was already in progress during the planning phase).
However, the resource may end up needing to edit the left work field while acting on the activity.