Race condition in mapping a node control in Pproto?

Questions
3

I’ve discovered the somewhat obscure feature (of the server protocol) that you can atomically initialize synth controls to bus numbers upon creation by using a string as the control value starting with the letter “c” or “a” followed by the (control or audio) bus number. Using this simplifies the code and fixes the intial map failure, but the 1st [m]env still doesn’t quite work properly; at least the following ones work ok now though.

(p = Pproto({ var onres;
	a = ~ampBusNum = ((type: \controlBus, channels: 1).yield)[\out];
	("c" ++ ~ampBusNum).postln;
	onres = (type: \on, instrument: \beep, amp: ("c" ++ ~ampBusNum), freq: 660).yield;
	onres.postln;
	~egroup = (type: \group).yield;
	~egroup.postln;
}, Pbind(
	\instrument, \menv,	\addAction, 1, \group, Pkey(\egroup), \out, Pkey(\ampBusNum),
	\dur, Pseq([4.2], inf),
	\legato, Pseq([0.5, 0.7, 0.9, 0.975, 1, 1.1, 1.151])
)).trace.play);