Up until the latest nightly, and in previous versions, a config file like:

verbose=vv

was accepted by mongod. With the latest nightly, it reports an error:

$ ./mongod --config /tmp/config.bad
Error parsing command line: BadValue Error parsing INI config file: in option 'verbose': invalid bool value
use --help for help

The docs don't say that this will work, but one of our Jenkins scripts was using this syntax and started failing a few days ago when the latest nightly was pushed.