Great. Problem solved: i had to install and use the US keyboard instead of US international. Thanks!
On the US-International keyboard, the apostrophe and quote key is a 'dead' key - that is, it doubles as the acute and umlaut diacritic marks, so that if you type (for example)
" then
a, you'll get
ä. To get the apostrophe or quote, press the key, followed by space.
If QB64 doesn't honor the system settings for keyboard and/or code page, you may get anomalous results - but I never had a problem with older versions.