Chart board unable to handle clearing of remaining estimate

We have been investigating a difference in the remaining estimates shown by the Greenhopper task board and chart board, and it looks like the interpretation of a cleared remaining estimate field isn't handled proberly in the chart board view.

I have attached a dump of the change view for a corrupt issue together with the chart board data export for the issue.

It appears that a clearing af a remaining estimate field freezes the remaining estimate before the clearing in the Chart board models, and isn't updated after this, even if the remaining estimate value is set again.