[Evolution] Refreshing a vfolder

[Thomas Frayne <tomf sjpc org>]

Periodically the vfolders seem to re-apply the criteria, and refresh
themselves.  I would like to be able to refresh the vfolders on demand. 
For example, with a vfolder containing my important, recent, and unread
messages.  When I mark a block of messages that are not important and
not recent as read, I want the messages to disappear from the vfolder. 
Sometimes the refresh occurs, sometimes not.

The only way I know to be sure that all vfolders are refreshed is to
exit Evolution and restart.  This requires a long wait while vfolders
are being built.  Also, I can usually refresh a single vfolder by using
the Virtual folder editor to change something in the definition of the
vfolder.

How can I force a single vfolder to be refreshed?  Under what
circumstances is a vfolder refreshed?