I have no idea what caused this or if its even a fault on my part. I'm not sure what other information should I post, so please ask away. If anyone could lend a hand, that'll be great.
I note that the Moment theme page (to which you linked), is running under TW5.1.13. The most recent release is TW5.1.22. There have been plenty of changes between those two versions, including updates to TWCore stylesheets.
So, let's start with a few questions:
1) what version of TW are you using?
2) what OS and browser are you using?
3) can you post your actual TW somewhere online so we can look at it ourselves?
-e