I found a comment in one of my environment files reminding me how to prevent commands prefixed with a space from being logged in BASH's history file:
export HISTIGNORE="&:[ ]*:exit"
Fortunately the comment pointed me back to the original source of the trick:
The Definitive Guide to Bash Command Line History - good coders code, great reuse
Let me teach you how to work efficiently with command line history in bash.