ABY with buffer, weird problem

[z1]

Hey guys, i've just built an ABY with a (jack orman) buffer, i placed the buffer with a 2PDT between the input and the first 3PDT,
this is the layout i used for the ABY

now there's a weird problem, everything works fine but when i switch the buffer on the B output gives a bang and doesnt give any output...
A works fine though, and i notice the buffer adding a bit of sparkle which is nice...
what could be my mistake?
thanks!