Here we go... found it:
"Students holding a one-year graduate degree from a provincially accredited post-secondary educational institution in Canada (pursued full-time) after having obtained, within the prior two years, a degree or diploma from an accredited post-secondary educational/training institution will qualify for a three year work permit. This exception also applies to students who have left Canada temporarily between the graduations."
Source: http://www.cic.gc.ca/english/resources/manuals/op/op12-eng.pdf (page 29)