Boyd, I suspect you're using a Mac -- one with an old operating system maybe? Or writing (on a Mac) using a text editor that still uses the old ASCII encodings.
Try entering the Unicode number directly & see what happens. We use to see this with Mac-Windows interchanges, esp if you're using "smart quotes," which with ASCII were above ASCII 127. The only Standard was limited to 7-bit ASCII. Different encodings for 8-bit ASCII (above 128) for Mac & Windows. I would think all the newer OS's use Unicode rather than ASCII...
The straight up & down apostrophe is U+0027, but the "smart" (proper) one is U+2019
EDIT:
I forget the way to enter these in HTML, but there is an escape sequence that provides for them...