This subject has been discussed several times over the past few years. It's not TCMD-specific, and certainly not a v17 issue.
This is an interaction between Windows controls and the GUI framework (which is an extended wrapper over the Microsoft framework). TCMD is never notified that a new button has been added -- which is one reason I added the "Save to INI" option a while back. That option tells TCMD to enumerate the buttons (or other controls) on the toolbar and save them to TCMD.INI, including the ones added by Windows.
However, TCMD is also never notified about a right-click on the buttons added by Windows, so it cannot display a context menu or popup dialog to offer you a delete option. The only way you can get rid of it is to edit your TCMD.INI.