It's never normal for an app to crash, but of course, they do from time to time. I've never seen the shortcut disappear from the homescreen after an app crash, but then again, I'm not that surprised that it could happen. Which app(s) are you talking about? Are you sure they're updated to the latest version? Were they installed from Google Play, Amazon Appstore, or downloaded as an .apk file from some random website?