leap_cli doesn't log to configured logfile anymore

this is the Leapfile from the bitmask repo:

--- git/bitmask ‹master* M› » cat Leapfile                     
@platform_directory_path = '../leap_platform'
@log = "/var/log/leap/bitmask.log"

but nothing is written to this file during a deploy

(from redmine: created on 2016-01-13, closed on 2016-02-24, relates #7795)