Incorrect Time Remaining calculation?

One of my stakeholders reported a problem to me, that when adjusting the estimate (in his case from 6 w to 8 w), the time remaining is changed incorrectly.

For example, I have a task and I say Estimate is 3w .. time remaining changes to 3w.  I change estimate to 6w, it changes time remaining to 6w (okay, this works how I would imagine).  I save this.

Then I have gone in and in the Correction field, I put 8 w.  My time remaining changes to 2w 1d.  How is that possible?   Can someone explain how the Time Remaining field is calculated within a given work item (like Task) based on the Estimate and Correction values entered? 

Does it take into account what is already in the Time Remaining field?    For example, estimate 6w, then correction to 7w (updates time remaining to 7w).  If I then change correction to 8w, does it say that 8w (correction) minus 6w (estimate) = 2w longer.  Since the Time Remaining field previously said 7w, then I add 7w to the additional time to make 9w?