I uploaded a .html into Design Studio and it worked as intended and rendered (I was pretty suprised by this)Have you tried just uploading it to Design Studio?
Just did some testing on a campaign and it seems you're correct. I find it very odd that Marketo would split the URL up in such a way that made it unable to see the query string to...
Good reply, most of the time it's the cache/cookie.I've noticed that by deleting a few specific cookies I can trigger the campaign to load the new content.