Although FTM indicates that I need to do a sync, when I execute the Sync option either from the main screen or from the Plan screen, I get the following message on the Change Log:
"The changes in this sync update are related to general tree structure and are not specific to data for people, media or sources.
These changes are needed to bring the trees into sync"
This is despite the fact that I have added several new members to the tree on FTM.
If I make changes (I just added a family member) online to the tree at Ancestry.com, and do a sync the Change Log shows that there was an addition and the sync happily occurs with that member added into my FTM.
Sync only appears to be working if changes are made to the online tree.