Looking at the source and some experiments, it appears EasyTimeline assumes 2 or 3 characters followed by a colon is always an interwiki link.
It doesn't actually have to do anything for interwiki links.
MediaWiki handles it so for example:
http://en.wikipedia.org/wiki/de:Berlin redirects to
http://de.wikipedia.org/wiki/Berlin
while
http://en.wikipedia.org/wiki/DmC:_Devil_May_Cry
is an English article since dmc is not an interwiki prefix.

Huon's fix [[:DmC: Devil May Cry]] only worked because it has 4 instead of 3 characters before a colon, and not because it starts with a colon.
http://en.wikipedia.org/wiki/OT:_Our_Town is an English article but [[OT: Our Town]] and [[:OT: Our Town]] would both fail in EasyTimeline. [[OT%3A Our Town]] would work, but would need a piped link to avoid an ugly display.