angle(x,y) function gives different result?

I was verifying my math against simulation (PSICE) results and noticed an odd discrepancy when trying to plot the difference in phase angle between two transfer functions.

Comparing each transfer function's phase angle to its corresponding simulation result shows an almost exact alignment. However, comparing the difference between the phase angles shows correctly (or at least as expected) only for the simulation results.

What am I missing? Worksheet is attached (MathCAD 15.0 M050).