Multi Trend Plot only works "correctly" the first time it is opened

I can select multiple points in Hierarchy and then use Multi Trend to view them.  This works great. In the plot below, I highlighted the IMx1 Node and then opened the Multi Trend

I want to then be able to go back to the Hierarchy and select different multiple points and have the Multi Trend display these points.  It does not currently do this.  This is with the same Multi Trend plot still open, but I went and shift selected all points under the next IMx1 Node.