In the doc page for 'vstaudio', there is this paragraph:

"vstaudio is used within an instrument definition that contains a 
vstmidiout or vstnote opcode. It outputs audio for only that one 
instrument. Any audio remaining in the plugin after the end of the note, 
for example a reverb tail, will be cut off and should be dealt with 
using a damping envelope".

But in the example given, vstaudio is used in an instrument that
does not contain vstmidiout, or vstnote.  This instrument #3 seems
to be used as I would expect vstaudiog to be used, according to
the documentation:

"vstaudiog (vstaudio global) is used in a separate instrument to process 
audio from any number of VST notes or MIDI events that share the same 
VST plugin instance (instance). The vstaudiog instrument must be 
numbered higher than all the instruments receiving notes or MIDI data, 
and the note controlling the vstplug instrument must have an indefinite 
duration, or at least a duration as long as the VST plugin is active".

Thanks,

Toby