I'm sorry but I still cannot reproduce that issue. Perhaps there are other things happening or other settings that are affecting this. Please provide a complete sample that demonstrates the problem and we can look into this further. With regards to the margin I'm not sure that is required to be handled by the style but I will submit an issue for it so it can be investigated.

I'm using version 9.2.

                        <r:ApplicationMenu.FooterToolbar>
                            <r:ApplicationMenuFooterToolbar>
                                <r:ButtonTool Id="Options" Command="{StaticResource Options}"
                                              Caption="Opt_ions" SmallImage="/Images/Small/Options.png">
                                    <r:ButtonTool.ToolTip>
                                        <r:XamRibbonScreenTip Header="Options" />
                                    </r:ButtonTool.ToolTip>
                                </r:ButtonTool>
                                <r:ButtonTool Id="Exit" Command="{StaticResource Exit}"
                                              Caption="E_xit" SmallImage="/Images/Small/Exit.png" Margin="8,0,0,0">
                                    <r:ButtonTool.ToolTip>
                                        <r:XamRibbonScreenTip Header="Exit" />
                                    </r:ButtonTool.ToolTip>
                                </r:ButtonTool>
                            </r:ApplicationMenuFooterToolbar>
                        </r:ApplicationMenu.FooterToolbar>

Also please notice the Margin property (which should really be set in the theme).