When showConnectingLines=false is set, the last node in each subtree has a background image rendered next to it. The URL for the image is something like: /a4j_3_1_0-SNAPSHOTorg.richfaces.renderkit.html.images.TreeLineLastImage/DATB/eAH7....1Tv3GRgYACS3BY4_.jsf.
This issue only appears in Firefox. It looks fine with IE6.
I have a screenshot I intend to attach.