It is possible to get a clutch slipping by a very aggressive start when otherwise it will handle the full torque of the engine with no problems. Take the scenario that you accelerate to the limiter in 1st gear and then quickly snatch second. The engine may be up at 6500 RPM and there is a serious amount of energy stored in the rotation of the flywheel and crankshaft.
In second the revs may drop to say 5000 RPM (not sure how big a jump there is between 1st and 2nd on a manual Omega). If you are quick you'll have grabbed second and released the clutch before the engine has slowed significantly. The difference in speed between the clutch plates is 1500 RPM. That can't disappear immediately due to the huge energy that needs to be dissipated to slow the flywheel. It must be dissipated by one of the two friction surfaces in the system - between the tyres and the ground or betweeen the clutch plates. If traction was good, maybe the clutch plates started slipping in this instance. It's a toss up between how much torque either friction surface can handle.
My experience is that once a clutch slips a little in this instance, it will continue to slip under engine torque for a second or two before biting, maybe because of heat buildup on the friction material.
Kevin