tmate: cannot mark transaction as read

With the right pane grouped by user, I open a user and see several
transactions. I select one, right click and select "Mark as Read". No
change. I press "Space" and the transaction is then marked as read (ie,
it is greyed).

(Don't know the exact version number, but I updated today. I clicked the
help button to try to get the version but got sent to the website. Maybe
the help button should popup a dialog with version info and a link to
the website.)