Well, I came across [link|http://asp.silvercloudsoftware.com/handmark/pages/answer.jsp?id=489|this] while digging around the web. The summary is that there is no HotSync conduit provided for synchronizing Mobile-DB and Mobile-DB-PC. As such, all Mobile-DB *.pdb files are "synchronized" using the System conduit which is more limited as you have found. The link provides instruction on how to simulate a two-way synchronization if you so desire.

The Mobile-DB knowledgebase is [link|http://asp.silvercloudsoftware.com/handmark/pages/question_c.jsp?category_id=9&more=Y&qas=on&trees=on&docs=on?|here].