I'm pretty sure that this has always worked like this. The practice accounts log themselves out after 30 minutes of inactivity but not sooner. This allows people to use a practice account without being booted off by someone else trying to sign up for a practice account and using the same login name. The timeout length is determined I believe by
# $sessionKeyTimeout defines seconds of inactivity before a key expires
$sessionKeyTimeout = 60*30;
in the file conf/defaults.config
You could override it in localOverrides.conf
Hope this helps.