pyocd-gdbserver crash when disconnecting serial port

If I start pyocd-gdbserver, run application and open serial port connection to mbed (K64F) board everything seems work as expected, but if I then disconnect serial port pyocd-gdbserver crashes with Unhandled exception in handleMsg.

See traceback below:

2017-05-17T11:55:03.547Z - warn: pyocd:stderr:  ERROR:root:Unhandled exception in handleMsg: 
2017-05-17T11:55:03.547Z - warn: pyocd:stderr:  Traceback (most recent call last):
2017-05-17T11:55:03.547Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/gdbserver/gdbserver.py", line 426, in handleMsg
2017-05-17T11:55:03.547Z - warn: pyocd:stderr:      return self.getRegisters(), 0
2017-05-17T11:55:03.547Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/gdbserver/gdbserver.py", line 868, in getRegisters
2017-05-17T11:55:03.547Z - warn: pyocd:stderr:      return self.createRSPPacket(self.target_facade.getRegisterContext())
2017-05-17T11:55:03.547Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/gdbserver/context_facade.py", line 54, in getRegisterContext
2017-05-17T11:55:03.547Z - warn: pyocd:stderr:      vals = self._context.readCoreRegistersRaw(reg_num_list)
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/debug/context.py", line 117, in readCoreRegistersRaw
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:      return self._core.readCoreRegistersRaw(reg_list)
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/coresight/cortex_m.py", line 655, in readCoreRegistersRaw
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:      reg_cb = self.readMemory(CortexM.DCRDR, now=False)
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/coresight/cortex_m.py", line 397, in readMemory
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:      result = self.ap.readMemory(addr, transfer_size, now)
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/coresight/ap.py", line 162, in readMemory
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:      self.write_reg(AP_REG['TAR'], addr)
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/coresight/ap.py", line 103, in write_reg
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:      self.dp.writeAP((self.ap_num << APSEL_SHIFT) | addr, data)
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/coresight/dap.py", line 259, in writeAP
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:      self.link.write_reg(ap_reg, data)
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py", line 635, in write_reg
2017-05-17T11:55:03.548Z - warn: pyocd:stderr:      self._write(dap_index, 1, request, [value])
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py", line 840, in _write
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:      self._send_packet()
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py", line 783, in _send_packet
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:      self._read_packet()
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py", line 738, in _read_packet
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:      decoded_data = cmd.decode_data(raw_data)
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py", line 419, in decode_data
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:      data = self._decode_transfer_data(data)
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:    File "/Users/user01/git/github/mbedmicro/pyOCD/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py", line 318, in _decode_transfer_data
2017-05-17T11:55:03.549Z - warn: pyocd:stderr:      raise DAPAccessIntf.TransferError()
2017-05-17T11:55:03.551Z - warn: pyocd:stderr:  TransferErro

Reproduce the crash by disconnecting the serial port while pyocd-gdbserver is running, then trace the request from pyOCD/gdbserver/gdbserver.py through context_facade.py, debug/context.py, coresight/cortex_m.py, and pyDAPAccess/dap_access_cmsis_dap.py. Determine how the reported TransferError should be handled so the server does not crash, and verify that the disconnect scenario completes without an unhandled exception.