On March 27 (incident posted by TSB April 25) an ExpressJet CRJ700 (N754EV), operating as flight ASQ5249, was inbound to CYYZ Toronto from KATL Atlanta. After landing on Runway 24L ASQ5249 was instructed by ATC to exit on taxiway D4 and hold short of runway 24R. The hold short instruction was read back by the flight crew. Shortly thereafter an ExpressJet EMB145, operating as flight ASQ4605, was cleared to take-off on Runway 24R. While ASQ4605 was on the take-off roll ATC observed ASQ5249 crossing the hold short line and instructed them to stop. ASQ5249 stopped just before the edge of Runway 24R. ASQ4605 became airborne while passing taxiway D2.