Avoiding "bus stealing" with busses/groups/Ppar

Questions
1

I’m running into some difficulties routing sounds through feedback busses and synths “stealing” the bus audio. The following example illustrates:

(
// Simple feedback delay line
add(SynthDef(\bustest,{ arg in,out,rate=0.2,fb=0.5,pan=0.5;
	var a = CombC.ar(InFeedback.ar(in,2),rate,rate,0) * fb;
	Out.ar(out,a);
	Out.ar(in,a);
}));
//Delay reading from bus 10, outputting to bus 12, shorter
Synth.new(\bustest,[\in,10,\out,12,\rate,0.5]);
//Delay reading from bus 12, outputting to main, longer
Synth.new(\bustest,[\in,12,\rate,1]); 
play(Ppar([
	//Higher line goes to bus 10, which gets "stolen" by ...
	Pbind(\freq,Pseq([440],inf), \dur, 1, \out,10)
	//Lower line, hijacking bus 12. 
	,Pbind(\freq,Pseq([220,Rest(1)],inf), \dur, 3, \out,12)
]));
)

The intent is for the second line to mix into bus 12 instead of replacing it.

2

Fixed with group assignments

(
var g1 = Group.new, g2 = Group.after(g1);

// Simple feedback delay line
add(SynthDef(\bustest,{ arg in,out,rate=0.2,fb=0.5,pan=0.5;
	var a = CombC.ar(InFeedback.ar(in,2),rate,rate,0) * fb;
	Out.ar(out,a);
	Out.ar(in,a);
}));
//Delay reading from bus 10, outputting to bus 12, shorter
Synth.new(\bustest,[\in,10,\out,12,\rate,0.5],g1);
//Delay reading from bus 12, outputting to main, longer
Synth.new(\bustest,[\in,12,\rate,1],g2); 
play(Ppar([
	//Higher line goes to bus 10
	Pbind(\freq,Pseq([440],inf), \dur, 2, \out,10,\group,g2)
	//Lower line to bus 12 
	,Pbind(\freq,Pseq([220,Rest(1)],inf), \dur, 6, \out,12,\group, g2)
]));
)