problem when setting cursor position property

I'm trying to use property nodes to set the cursor position programmatically, following an arrow keypress.  When my actual data file plotted, the position assignment doesn't work properly.  If I clear the data from the graph (right click, clear graph), then the cursor responds properly.  I've attached a zipped file with VI that demonstrates the problem.  Sorry the file is large--I had to include my data file to properly demonstrate the problem.

Thanks for any advice that help me clear this up,

Allan