After calculating folder sizes (cm_CountDirContent), if any of the folders in question are being written to,Config | Refresh:
Auto-Refresh when the file system changes:
[X] Refresh when files are created, deleted and renamed.
[X] Also when size, date, or attributes change.
[X] Don't react to updates while in the background.
[X] Update footer (total number of files)
then the size calculation gets cleared and goes back to < DIR >.
Not sure if this qualifies as a bug, or a (mis)feature, but its definitely annoying. . .
Perhaps an asterisk could be added to the size calculation to indicate it has changed, instead of clearing it completely?