mh cleanup error with no good way to debug

[marcmerlin]

Every time mh errors in some way, I now get these extra lines and cna't tell what serial port it's unhappy about:
(in cleanup) Can't call method "setcflag" on an undefined value at ../lib/site/Device/SerialPort.pm line 452 during global destruction.
at ./mh line 31.
main::ANON("Can't call method "setcflag" on an undefined value at ../lib/"...) called at ../lib/site/Device/SerialPort.pm line 452
Device::SerialPort::write_settings(Device::SerialPort=HASH(0xa7518cc)) called at ../lib/site/Device/SerialPort.pm line 1926
Device::SerialPort::close(Device::SerialPort=HASH(0xa7518cc)) called at ../lib/site/Device/SerialPort.pm line 1958
Device::SerialPort::DESTROY(Device::SerialPort=HASH(0xa7518cc)) called at ./mh line 0
eval {...} called at ./mh line 0
(in cleanup) Can't call method "setcflag" on an undefined value at ../lib/site/Device/SerialPort.pm line 452 during global destruction.
at ./mh line 31.
main::ANON("Can't call method "setcflag" on an undefined value at ../lib/"...) called at ../lib/site/Device/SerialPort.pm line 452
Device::SerialPort::write_settings(Device::SerialPort=HASH(0xa6ddd34)) called at ../lib/site/Device/SerialPort.pm line 1926
Device::SerialPort::close(Device::SerialPort=HASH(0xa6ddd34)) called at ../lib/site/Device/SerialPort.pm line 1958
Device::SerialPort::DESTROY(Device::SerialPort=HASH(0xa6ddd34)) called at ./mh line 0
eval {...} called at ./mh line 0
(in cleanup) Can't call method "setcflag" on an undefined value at ../lib/site/Device/SerialPort.pm line 452 during global destruction.
at ./mh line 31.
main::ANON("Can't call method "setcflag" on an undefined value at ../lib/"...) called at ../lib/site/Device/SerialPort.pm line 452
Device::SerialPort::write_settings(Device::SerialPort=HASH(0xa53fdcc)) called at ../lib/site/Device/SerialPort.pm line 1926
Device::SerialPort::close(Device::SerialPort=HASH(0xa53fdcc)) called at ../lib/site/Device/SerialPort.pm line 1958
Device::SerialPort::DESTROY(Device::SerialPort=HASH(0xa53fdcc)) called at ./mh line 0
eval {...} called at ./mh line 0