The screenshot looks an awful lot like MS Outlook...are you certain that the screenshot you posted is of our UltraExplorerBar? I implemented the collapsible navigation pane stuff and I am at a loss for how an ink button could be appearing there. If you can, please provide details about what properties are set on the UltraExplorerBar.
I am speculating a bit here, but it would seem possible that the Vista machine is ink-enabled (i.e., a tablet PC), and you have an UltraInkProvider on the form. If this is the case, you can set the ShowInkButton property of the UltraInkProvider to false, or possibly set its Enabled property to false. I am surprised to see an ink button on the navigation pane header of UltraExplorerBar; to my knowledge that is not an editable entity and as such should not be showing an ink button regardless of whether inking is enabled.