Unfortunatelly that's how LFS now works with sequential gearbox without ignition cut (I recall having "random" downshift denials with Raybeam,which also has same type),nothing we can do about. The specific type was selected because it was simply the most clutch saving - both H-shifter and sequential with ignition cut tended to overheat clutch even more,while paddle shift is simply unrealistic for this type of car.
It is the same gearbox you might be used from FBM - you always must unload gearbox (in most cases by lifting throttle,sometimes going over bump during shift can help) for upshift,dowshifts can also be affected by loads.
