Broken URL when creating a new page

Perch: 3.0.13
Production mode: Production (100)
Installed apps: content (3.0.13), assets (3.0.13), categories (3.0.13), perch_forms (1.10)
DB driver: PDO
DB tables: perch3_categories (0), perch3_category_counts (0), perch3_category_sets (0), perch3_content_index (342), perch3_content_items (172), perch3_content_regions (27), perch3_forms (1), perch3_forms_responses (2), perch3_menu_items (9), perch3_navigation (2), perch3_navigation_pages (30), perch3_page_templates (3), perch3_pages (12), perch3_resource_log (1466), perch3_resource_tags (28), perch3_resources (296), perch3_resources_to_tags (38), perch3_settings (23), perch3_user_passwords (0), perch3_user_privileges (32), perch3_user_role_privileges (2), perch3_user_roles (2), perch3_users (4)
Users: 4
App runtimes:
<?php
    $apps_list = array(
        'content',
        'categories',
        'perch_forms',
    );
?>
Editor plug-ins: ckeditor
H1: edf5a7e5ce1d736be8c5c68459e4a835
L1: 79c92d830e4949be3310e4ae8a72b601
F1: 3b606135b33e6a102526838f4152a807
headerColour: #beaae3
content_singlePageEdit: 1
helpURL:
siteURL: /
hideBranding: 1
content_collapseList: 1
lang: en-gb
installedAt: 3.0.10
update_3.0.10: done
latest_version:
on_sale_version: 3.0.13
headerScheme: light
dashboard: 1
hide_pwd_reset: 0
keyboardShortcuts: 0
content_hideNonEditableRegions: 0
content_frontend_edit: 0
content_skip_region_list: 0
assets_restrict_buckets: 0
logoPath: /cms/resources/test-logo.jpg
update_3.0.11: done
sidebar_back_link: 1
update_3.0.13: done
PERCH_DEVELOPMENT: 10
PERCH_STAGING: 50
PERCH_PRODUCTION: 100
PERCH_DB_USERNAME: test_perch3
PERCH_DB_SERVER: testtow.dns-systems.net
PERCH_DB_DATABASE: test_perch3
PERCH_DB_PREFIX: perch3_
PERCH_TZ: UTC
PERCH_EMAIL_FROM: info@test.co.uk
PERCH_EMAIL_FROM_NAME: Test
PERCH_LOGINPATH: /cms
PERCH_PATH: /www/cms
PERCH_CORE: /www/cms/core
PERCH_RESFILEPATH: /www/cms/resources
PERCH_RESPATH: /cms/resources
PERCH_EMAIL_METHOD: smtp
PERCH_EMAIL_HOST: smtp.gmail.com
PERCH_EMAIL_PORT: 587
PERCH_EMAIL_AUTH: 1
PERCH_EMAIL_SECURE:
PERCH_EMAIL_USERNAME: test@test.test.co.uk
PERCH_HTML5: 1
PERCH_RUNWAY:
PERCH_ERROR_MODE: DIE
PERCH_DATE_LONG: %d %B %Y
PERCH_DATE_SHORT: %d %b %Y
PERCH_TIME_SHORT: %H:%M
PERCH_TIME_LONG: %H:%M:%S
PERCH_RUNWAY_ROUTED:
PERCH_STRONG_PASSWORDS:
PERCH_ASSET_VERSION: f704e7442d11292c99b5
PERCH_DEBUG:
PERCH_PREVIEW_ARG: preview
PERCH_TEMPLATE_PATH: /www/cms/templates
PERCH_TEMPLATE_FILTERS:
PERCH_DEFAULT_DOC: index.php
PERCH_DEFAULT_EXT: .php
PERCH_PRODUCTION_MODE: 100
PERCH_XHTML_MARKUP:
PERCH_RWD: 1
PERCH_HTML_ENTITIES:
PERCH_SSL:
PERCH_STRIPSLASHES:
PERCH_PROGRESSIVE_FLUSH: 1
PERCH_PARANOID:
PERCH_FORCE_SECURE_COOKIES:
PERCH_DEFAULT_BUCKET: default
PERCH_TRANSLATION_ASSIST:
PERCH_PASSWORD_MIN_LENGTH: 6
PERCH_MAX_FAILED_LOGINS: 10
PERCH_AUTH_LOCKOUT_DURATION: 1 HOUR
PERCH_VERIFY_UPLOADS:
PERCH_PRIV_ASSIST:
PERCH_CUSTOM_EDITOR_CONFIGS:
PERCH_ENABLE_EXIF: 1
PERCH_AUTH_PLUGIN:
PERCH_DB_CHARSET: utf8
PERCH_DB_PORT:
PERCH_DB_SOCKET:
PERCH_APPS_EDITOR_PLUGIN: markitup
PERCH_APPS_EDITOR_MARKUP_LANGUAGE: markdown
Hosting settings
PHP: 5.6.31
Zend: 2.6.0
OS: Linux
SAPI: apache2handler
Safe mode: not detected
MySQL client: 5.6.36
MySQL server: 5.6.36
Free disk space: 433.02 GB
Extensions: Core, date, ereg, libxml, openssl, pcre, sqlite3, zlib, bcmath, bz2, calendar, ctype, curl, dbase, dom, hash, fileinfo, filter, ftp, gd, gettext, gmp, SPL, iconv, imagick, session, intl, json, mailparse, mbstring, mcrypt, standard, imap, memcached, mssql, mysql, mysqli, OAuth, PDFlib, PDO, pdo_mysql, pdo_sqlite, pspell, Reflection, SimpleXML, soap, ssh2, exif, tidy, tokenizer, wddx, xml, xmlreader, xmlrpc, xmlwriter, xsl, zip, memcache, apache2handler, mhash, ionCube Loader, Zend Guard Loader, Zend OPcache
GD: Yes
ImageMagick: Yes
PHP max upload size: 128M
PHP max form post size: 128M
PHP memory limit: 256M
Total max uploadable file size: 128M
Resource folder writeable: Yes
Session timeout: 24 minutes
Native JSON: Yes
Filter functions: Yes
Transliteration functions: Yes
UNIQUE_ID: WmuCSlPfah4AAAMtF1gAAAAY
HTTP_HOST: localhost
HTTP_CONNECTION: keep-alive
HTTP_UPGRADE_INSECURE_REQUESTS: 1
HTTP_USER_AGENT: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36
HTTP_ACCEPT: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
HTTP_REFERER: https://localhost/cms/core/settings/diagnostics/
HTTP_ACCEPT_ENCODING: gzip, deflate
HTTP_ACCEPT_LANGUAGE: en-GB,en-US;q=0.9,en;q=0.8,pl;q=0.7
HTTP_COOKIE: _ga=GA1.3.738087583.1516023715; cmsa=1; PHPSESSID=s2k8h416u26v5eclvg9himrjl3
PATH: /sbin:/usr/sbin:/bin:/usr/bin
SERVER_SIGNATURE: <address>Apache Server at localhost Port 80</address>
SERVER_SOFTWARE: Apache
SERVER_NAME: localhost
SERVER_ADDR: 83.223.101.30
SERVER_PORT: 80
REMOTE_ADDR: 92.103.30.122
DOCUMENT_ROOT: /www/
SERVER_ADMIN: postmaster@localhost
SCRIPT_FILENAME: /www/cms/core/settings/diagnostics/index.php
REMOTE_PORT: 15562
GATEWAY_INTERFACE: CGI/1.1
SERVER_PROTOCOL: HTTP/1.1
REQUEST_METHOD: GET
QUERY_STRING: extended
REQUEST_URI: /cms/core/settings/diagnostics/?extended
SCRIPT_NAME: /cms/core/settings/diagnostics/index.php
PHP_SELF: /cms/core/settings/diagnostics/index.php
REQUEST_TIME_FLOAT: 1516995146.171
REQUEST_TIME: 1516995146

Yes that's the report from the problematic server. Some sensitive details has been hidden.

Now when you asked I've tried it at IE, Chrome and FF with the same result.

Does anything cross your mind? Could this encoding be related to some server settings? From my understanding that's a piece of JavaScript behind it however it's strange that it behaves that way - it never happened to me before.

Yes that's the case. No problem, I'll let you know if I get to the bottom of it. Thanks for your input