the merc window itself is fine, however yes in order to recall your merc from your character window is the issue. it is currently required to /merc resume in order to recall your merc at the moment. hope this helps, cheers!
Last few days I am unable to use the merc window.
The Hire button now says $hire$ instead, and clicking it does nothing.
I have to use /merc_resume and /merc_suspend.
Only the Updater itself has been updated so far at this time. I suspect he'll push quite a few updates out here in the near future according to some of his other posts and will document which specific UI files have been updated when that happens.