there could be a preference to do a "Sheet out" when its done cutting, or OMEGA could be set to cutoff after the job, butthe procedure isn't working right. check your prefs in GSPPlot under device select and see if anything looks out of place.
you can also upgrade your 2.5 to the last 2.6 revision off of Gerbers webpage. there may be a glitch somewhere in Omega thats been fixed.