Turns out my caching software, which fixed the problems I was having with the site running slowly and consuming too much memory, was so diligent that it started instructing RSS readers to cache all my feeds. So, fixing one problem led to another.
Typical.
Fortunately, it was a very easy problem to correct once I found the problem, although finding it took hours.
I’m going to stay on Feedburner for now, but I am concerned that the service itself may be due for deprecation. So it’s likely that I’ll transfer the feed at some point, but when I do there will be an automatic redirect and most readers shouldn’t even notice.
Happy feed reading!