bzr @2.6.0_3: bzr merge with bzr+ssh no longer functions

[ianstyxial]

The port bzr @2.6.0_3 (active) on macOS 10.13.6 the bzr merge with bzr+ssh no longer functions. Indeed, if I run

$ bzr merge bzr+ssh://pi@lyra/~/AVision/

I get the error messages as in the attached file, starting with

Merging from remembered submit location bzr+ssh://pi@lyra/~/AVision/
bzr: ERROR: exceptions.SyntaxError: invalid syntax (signing.py, line 32)

bzr has worked fine for years with bzr+ssh, but I recently upgraded to the latest port of Bazaar on macOS 10.13.6, and I ran into this issue.

Check version:

sh-3.2# port installed bzr
The following ports are currently installed:
  bzr @2.6.0_3 (active)

Indeed:

bash-3.2$ bzr --version
Bazaar (bzr) 2.6.0
  Python interpreter: /opt/local/Library/Frameworks/Python.framework/Versions/2.7/Resources/Python.app/Contents/MacOS/Python 2.7.18
  Python standard library: /opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7
  Platform: Darwin-17.7.0-x86_64-i386-64bit
  bzrlib: /opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/bzrlib
  Bazaar configuration: /Users/ian/.bazaar
  Bazaar log file: /Users/ian/.bzr.log

[ianstyxial]

standard output, including error messages of bzr merge, using bzr+ssh