I didn't realize this was happening, but someone reported several days ago that nothing had changed on our site for 4 days. I thought he was looking at a different site, since we have new posts and comments every day.
Just now, I was on the forum for support of my theme, Weaver II Pro, and a couple forum members saw a page that was current 4 days ago! (And, no, I'm not using an old version of PHP)
I disabled Quick Cache, and they could immediately see the current page.
It seems that the free version of Quick Cache has not been functioning well for quite a number of people since the "Pro" version came out. Now I don't mind at all paying $15.00 for extra features in a Pro version, but a misbehaving plugin does not inspire confidence in a "Pro" version. In my case, I paid for a "Pro" version of a misbehaving plugin several months ago, and the Pro version is as buggy, if not worse. Once bitten, twice shy!
Serving up a stale page for four days is a serious issue!! And removing functionality from a free version in order to sell a Pro version seems a bit out of harmony with the spirit of the WordPress community.
Seeing there are so many issues with Quick Cache now, it seems I have no option but to change over to Super Cache. So sorry ...