How do I keep the vertical arrow connected in a text arrow annotation?

When trying to add an text arrow to a plot I can get the text arrow to show up on the plot but the line is disconnected from the arrowhead.

x=1:.1:10;
y1 = sin(x*pi)/10;

figure
plot(x,y1)
tb = annotation('textarrow','String','Stim');
annoAx = gca;
tb.Parent = annoAx;
yRange = annoAx.YLim(2) - annoAx.YLim(1);    
tb.Position = [5, .09, 0, -.04];

The problem seems to go away if the arrow is not perfectly vertical or if the y values are larger. Any suggestions?

PS I am using MATLAB R2014b