It seems that in some circumstances PUTting a calendar entry towards a Radicale Calendar server fails. Radicale does not consider the Content valid, since the "Content-Type:"-Header seems to be empty.

This is some debug-output I added to radicale dumping the request for a (working) refresh (trimmed for some information containing sensitive or useless information):

{'HTTP_AUTHORIZATION': '********',
 'SERVER_PROTOCOL': 'HTTP/1.1',
 'SERVER_SOFTWARE': 'WSGIServer/0.1 Python/2.7.14',
 'SCRIPT_NAME': '',
 'REQUEST_METHOD': 'PROPFIND',
 'QUERY_STRING': '',
 'HTTP_CONNECTION': 'close',
 'SERVER_NAME': '******',
 'REMOTE_ADDR': '**.**.**.**',
 'HTTP_DEPTH': '0',
 'wsgi.url_scheme': 'http',
 'SERVER_PORT': '****',
 'CONTENT_LENGTH': '113',
 'HTTP_PRAGMA': 'no-cache',
 'wsgi.input': <socket._fileobject object at 0x7f704afb8cd0>,
 'HTTP_USER_AGENT': 'Evolution/3.26.0',
 'HTTP_HOST': '*******:****',
 'wsgi.multithread': True,
 'HTTP_CACHE_CONTROL': 'no-cache',
 'wsgi.version': (1, 0),
 'GATEWAY_INTERFACE': 'CGI/1.1',
 'wsgi.run_once': False,
 'wsgi.multiprocess': False,
 'HTTP_ACCEPT_LANGUAGE': 'en-gb, en;q=0.9, en;q=0.8',
 'CONTENT_TYPE': 'application/xml; charset="utf-8"',
 'wsgi.file_wrapper': <class wsgiref.util.FileWrapper at 0x7f704b03db48>,
 'REMOTE_HOST': '******',
 'wsgi.errors': <open file '<stderr>', mode 'w' at 0x7f704d0bf1e0>,
 'PATH_INFO': '/sync/<user>/calendar.ics/'}

Note that Radicale has no troubles with this request.

However, the PUT is missing the 'CONTENT_LENGTH'-information:

{'HTTP_AUTHORIZATION': '********',
 'SERVER_PROTOCOL': 'HTTP/1.1',
 'SERVER_SOFTWARE': 'WSGIServer/0.1 Python/2.7.14',
 'SCRIPT_NAME': '',
 'HTTP_TRANSFER_ENCODING': 'chunked',
 'REQUEST_METHOD': 'PUT',
 'QUERY_STRING': '',
 'HTTP_CONNECTION': 'close',
 'SERVER_NAME': '****',
 'REMOTE_ADDR': '**.**.**.**',
 'HTTP_IF_NONE_MATCH': '*',
 'wsgi.url_scheme': 'http',
 'SERVER_PORT': '****',
 'CONTENT_LENGTH': '',
 'HTTP_PRAGMA': 'no-cache',
 'wsgi.input': <socket._fileobject object at 0x7f704afb8cd0>,
 'HTTP_USER_AGENT': 'Evolution/3.26.0',
 'HTTP_HOST': '****:****',
 'wsgi.multithread': True,
 'HTTP_CACHE_CONTROL': 'no-cache',
 'wsgi.version': (1, 0),
 'GATEWAY_INTERFACE': 'CGI/1.1',
 'wsgi.run_once': False,
 'wsgi.multiprocess': False,
 'HTTP_ACCEPT_LANGUAGE': 'en-gb, en;q=0.9, en;q=0.8',
 'CONTENT_TYPE': 'text/calendar; charset="utf-8"',
 'wsgi.file_wrapper': <class wsgiref.util.FileWrapper at 0x7f704b03db48>,
 'REMOTE_HOST': '*****',
 'wsgi.errors': <open file '<stderr>', mode 'w' at 0x7f704d0bf1e0>,
 'PATH_INFO': '/sync/<user>/calendar.ics/67296f272f2b2d665321324ee45d8b51b4750abc.ics'
}

Since Content-Length is considered zero by radicale it does not try to read the actual content and the new calendar entry is not getting inserted.

I am not sure that evolution actually sent an empty content-length header, it also might be possible that it sent something that wsgi (or whatever) could not parse properly.

I suspect that the bug is in evolution, since the content-length for the PROPFIND request is properly interpreted by radicale.