Seems to be caused by the % character, throws a "malformed URI error" on Discuss as well.
URIError: malformed URI sequence mithril.js:1782
pt mithril.js:1782
g mithril.js:189
pt mithril.js:1780
RegExpGetFunctionalReplacement self-hosted:4741
RegExpLocalReplaceOptFunc self-hosted:5038
Symbol.replace self-hosted:4636
replace self-hosted:5508
pt mithril.js:1777
pt mithril.js:1618
s mithril.js:1637
route mithril.js:1641
mount Application.js:159
mount ForumApplication.js:99
boot Application.js:138
<anonymous> 62-hello-there%:117