A Google Web Search Help thread has confirmed reports of a bug with the Google Cache page.
Typically when you search for something and then click on the cached page, Google will highlight the word you searched for on the cached page, if it is on the page. But now, if you are trying to see the highlighted results you may not get it.
If you are signed into Google when searching, Google will not highlight the word. If you are signed out, Google will highlight the word.
I assume this has to do with the SSL search dropping query data to pass to Google's cache. But Googler, Sarah, made it sound like it is a temporary bug.
Thanks all for your detailed responses in reporting this. This is something that we are aware of and are looking into.
As you have found, for now, if you want to see the terms highlighted, you can do so by signing out.
Screen Shot of Highlighted Words When Signed Out of Google:
Screen Shot of No Highlighting in Google Cache When Signed In:
Again, I suspect this is related to the SSL change.
Forum discussion at Google Web Search Help.