Capacitive feedback in TL497 inverter circuit

[guymo]

I'm looking at an old device (Pearl Syncussion percussion synthesizer) which uses a TL497 to generate a -8V power supply. Some recent clone versions of this have experienced problems with the TL497 becoming very hot and I'm trying to figure out why.

The original schematic (attached) has a capacitor (C34) between the comparator input and the collector of the switching transistor and I am trying to figure out the impact of that. The TI app note http://www.ti.com/lit/an/slva143/slva143.pdf is very insistent that the voltage at the collector ought to be a sharp pulse wave, which seems unlikely with this cap in place. The same app note suggests using a diode for feedback to clamp the comparator input during the on-cycle -- schematic attached. It seems to me that using a cap in place of that diode will make matters worse rather than better.

What purpose does that capacitor serve, and would life be better with a diode there as suggested in the app note?

A related question: the datasheets suggest that one should not use the internal diode as a flyback when the device is employed in an inverting configuration; an external diode should be used instead. Any idea why?

[If this belongs in Beginners please accept my apologies! I thought it was perhaps a little too technical for that.]