[Mike Copioli]

Originally Posted by jmu465

A second and less obvious diode is common across the Vin and Vout pins of the regulator. This is a common design practice (but interesting left off the app note for the LM79L05) This diode protects from transients during power down. Imagine the device is powered up and then Vpwr is suddenly (0V) removed. This second protection diode is required to discharge the filter caps on the output by safely shunting the current around the regulator. Without this diode, the Vreg will be stressed with reversed polarity. VReg are hyper sensitive to any reverse voltage. As engineers we need to think beyond the "run" mode and also consider the power up and power down modes.

Excellent point, that is one reason why the 33uF cap is on the upstream side of the reg, that and to also filter out ripple.