Send a POST request with any content at all to a Parsoid URL containing a colon, and you'll get strange crashes. Strangely, the behavior differs between localhost and enwiki:

POST /localhost/VisualEditor%3AMetastuff HTTP/1.0
Host: localhost:8000
Content-Length: 3

HTTP/1.1 500 Internal Server Error
X-Powered-By: Express
Content-Type: text/html; charset=utf-8
Content-Length: 66
Connection: close

ParserError: Failed to parse the JSON response for Page Fetch null

(Note that I didn't even get a chance to send the POST body, the 500 occurs as soon as I send the double newline that terminates the request header.)

For this case, the Parsoid log shows:
ParserError: Failed to parse the JSON response for Page Fetch null
worker 10132 died, restarting.


POST /en/Talk%3AWQKO HTTP/1.0
Host: localhost:8000
Content-Length: 3

Foo

[Parsoid closes the connection without sending anything]

Parsoid log:
There was an error in the HTML5 parser! Sending it back to the editor.
Error: No source to parse
    at EventEmitter.parse (/var/lib/parsoid/Parsoid/js/node_modules/html5/lib/html5/parser.js:44:20)
    at /var/lib/parsoid/Parsoid/js/api/ParserService.js:579:6
    at /var/lib/parsoid/Parsoid/js/api/ParserService.js:284:4
    at /var/lib/parsoid/Parsoid/js/lib/mediawiki.parser.environment.js:185:3
    at [object Object].<anonymous> (/var/lib/parsoid/Parsoid/js/lib/mediawiki.parser.environment.js:209:4)
    at Array.1 (/var/lib/parsoid/Parsoid/js/lib/mediawiki.ApiRequest.js:60:4)
    at EventEmitter._tickCallback (node.js:192:40)
TypeError: Cannot read property 'childNodes' of undefined
    at /var/lib/parsoid/Parsoid/js/api/ParserService.js:597:34
    at /var/lib/parsoid/Parsoid/js/api/ParserService.js:284:4
    at /var/lib/parsoid/Parsoid/js/lib/mediawiki.parser.environment.js:185:3
    at [object Object].<anonymous> (/var/lib/parsoid/Parsoid/js/lib/mediawiki.parser.environment.js:209:4)
    at Array.1 (/var/lib/parsoid/Parsoid/js/lib/mediawiki.ApiRequest.js:60:4)
    at EventEmitter._tickCallback (node.js:192:40)

--------------------------
**Version**: unspecified
**Severity**: critical