Comment 3 for bug 692391

Have resolved this here by adding a line to sudoers (actually use a file in /ect/sudoers.d/ instead
Defaults !tty_tickets

The issue seems to be the configure option of --with-tty-tickets that was carried forward from sudo 1.7.2 but has a slightly different effect here in 1.7.4 - once the instance is closed the timeout ends
Because of no response don't know if this new behavior was the new intention or just one of those things, no big deal, easily 'fixed' for those that wish the old behavior back (in lieu of some other approach

Ex. here for those that wish to change in sudoers.d or if desiring to re-build sudo then just change the option in /debian/rules to --without-tty-tickets
http://ubuntuforums.org/showthread.php?p=10500211#post10500211