the charging system in cars lets alot of noise into the electrical system, which if you've ever installed an audio amp in a car you will know this is why you don't run the audio cables alongside the power cables; you will pick up the electrical noise in frequescy directly related to engine rpm.
In bikes, the output of the stator is much less than that of a car's alternator, which in a running car is more than enough to run all your electrical systems, the engine, charge the battery, and then some in the car.
Bikes not only regulate the output of the generator to a cleaner output, but the much more marginal output of it at idle speeds allows the battery to act as a filter for most of this, and when jump starting from a running vehicle, the drain caused by the bike isn't enough to cause the car's battery to act as a filter as the bike battery would, and introduces alot of noise. The biggest problem you will see will be unwillingness to keep running. By adding more load to the electrical system, you can reduce the noise and lessen its effects on the operation of the bike (highbeams, brake lights, blinkers).
Generally when you jump start a bike you want to have the external power source connected only long enough that the bike will remain running on its own. After you have it running you will want to keep the rpms above idle for a while to allow the battery to regain some charge (if the battery was drained and the charging system is working, and the battery is still ok)