That's just a "simple" treble bleed. Running a resistor across (parallel) the cap is Duncan style treble bleed, and running it in series with the cap is a Kinman style bleed.
You probably know this, but I'll add this for the casual reader...
As you turn the volume down, more resistance is added to the circuit. As the resistance goes up, higher frequency signal is filtered out, when the volume is all the way "off" - it really has just filtering out all the remaining signal. What that means is that as the volume is lowered, tone is lost. To keep some of the higher frequencies in the signal as you increase the resistance (i.e. lower the volume), you include a capacitor across the leads to the pot. Since a capacitor acts like an open circuit at higher frequencies, it will allow some of those higher frequencies to "bleed" out into the amp as the signal is being choked out by the volume pot.
Putting a resistor across the cap - the "Duncan" style mod - lowers the (effective) resistance value of your volume pot (it becomes two resistors in parallel with a capacitor). Less overall resistance means the volume does not turn off as quickly as it would otherwise. That gives you more room for subtle volume changes - the cap just allows the treble to bleed through as this happens.
Putting a resistor in line with the cap, (the Kinman style mod) also lowers the effective resistance of the volume put, but shapes where and how the volume tapers off - more of a swell at first, etc.
if you just put a cap across the volume pot leads - you have a very simple treble bleed, not changing the effective resistance of your volume pot, so it'll taper off as per usual, but because the treble bleeds through as it is being cut off - the effect is more abrupt.
Hope that helps.