Hi Kirsten,
I am guessing that you have a rule on the first topic that shows the second table. If you are using a formatting rule to control hide-show of the second table (or do a query), you may need to right click the topic field and go to browser and select to have it always post back. Why? Well, it may not be inferring correctly when it should run the logic.
Now that is just a guess. This kind of thing works for us all the time without any problems, and the browser post back setting is usually only an issue for buttons but maybe that is what you are seeing.
Please note: you cannot use master-detail sections in the browser. Guessing that isn't your issue though since it would complain on publish.
Good luck!