UnicodeDecodeError while exchanging with the server

Today at 2017-03-14 09:04:56,058 we started getting these errors in a r951 client broker log with every server exchange:

2017-03-14 09:04:56,061 ERROR [PoolThread-twisted.internet.reactor-0] Error contacting the server at https://edge.lscape.net/message-system.
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/landscape/broker/transport.py", line 73, in exchange
    message_api)
  File "/usr/lib/python2.7/dist-packages/landscape/broker/transport.py", line 47, in _curl
    headers=headers, cainfo=self._pubkey, curl=curl))
  File "/usr/lib/python2.7/dist-packages/landscape/lib/fetch.py", line 68, in fetch
    output = io.BytesIO(networkString(data))
  File "/usr/lib/python2.7/dist-packages/twisted/python/compat.py", line 492, in networkString
    s.decode('ascii')
UnicodeDecodeError: 'ascii' codec can't decode byte 0xae in position 23: ordinal not in range(128)

Checking upgrade logs, the client was upgraded to from r941 to r951 at around 09:03:51:

Start-Date: 2017-03-14 09:03:51
...
Upgrade: python-stripe:amd64 (376-0~landscape+1~ubuntu14.04.1, 378-0~landscape+1~ubuntu14.04.1), landscape-client:amd64 (17.02~bzr941-0ubuntu0~ubuntu14.04.1, 17.02~bzr951-0ubuntu0~ubuntu14.04.1), landscape-common:amd64 (17.02~bzr941-0ubuntu0~ubuntu14.04.1, 17.02~bzr951-0ubuntu0~ubuntu14.04.1)