Question: Unevaluated region when plotting a procedure

Hi -- I am trying to plot a (fairly basic) procedure, Q_plot, which defines a piecewise function (three pieces). Q_plot evaluates no problem at the command prompt for all three regions -- but only plots for two of the three regions. Resulting in a big hole in the middle of my graph! Hmm? I've uploaded a copy of the worksheet, with the plot (and the aformentioned hole in the middle). Thanks Here's the link to the worksheet: http://www.mapleprimes.com/files/5475_Diagnostic-proc-Q.mw
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