Read this:
http://help.adobe.com/en_US/encore/cs/using/WS74BC1059-66C3-46c5-9FA6-78DF1...
You can change button routing by turning automatic routing off.
Also, are any of your buttons set to autoactivate?
I assume that what you refer to as poster boards are what Encore calls thumbnails, where the content is set by selecting the poster frame for a chapter.
Stan Jones