Toucan 3.1.7 seems to remove directories unexpectedly

I have been using sync for years to copy data off my computer onto an external drive. This worked fine and would copy files over if they were new ore more recently modified at the source (and not change the target in any other way.)

With the update to Toucan 3.1.7 I have a lot of messages indicating my target directories had been removed (which as per help should just not happen in synch mode.)

Please advise
a) if this is a bug (and if so when will it be removed)
b) whether I should be using a different mode to create backups off my current source to a target that has the same structure as the current source

Thanks
Thomas