I have a button/link on my toolbar for Synchronize. (x64 Dopus) After I have completed a sync between directories/drives, clicking on Synchronize again, closes the sync panel and returns to what is apparently a default two column style lister - rather than whatever lister format I was using (usually explorer style). Previous versions always returned to my previous style...
It's (a little bit) annoying as I have to manually close the second column each time I finish using Synchronize...
Am I missing a switch somewhere in the preferences? Or is this a problem?
That's quite an old change, and the way it works now is by-design.
Opening the sync panel will switch on the second file display, if it is not already on (since you need both to do a sync).
Closing the sync panel just closes the sync panel. It no longer closes the second file display, since Opus has no way to know whether or not you actually wanted to keep it and use the folder which is now displayed in it. If you don't want it, just click the close button on the file display and it will go away. You should then be back to how you started.
If you want to, you can change your button to always close the second file display when closing the sync panel, but then you'd lose the file display in situations where you might still want it. It's up to you though.