endless loop: e.g. 2in2out -> balance (or 1in1out)
#23 0xb7ab5c17 in ARDOUR::Pannable::value_as_string
#24 0xb2ebb206 in ARDOUR::Pannerbalance::value_as_string
#25 0xb7ab5c17 in ARDOUR::Pannable::value_as_string
#26 0xb2ebb206 in ARDOUR::Pannerbalance::value_as_string
ad infinitum