Its an online sync thing. Your 'buddy' can only see the vehicle that you are actively using. I know this can be a little anoying from time to time. I for instance, like to put the jeep on top of a truck and just ride some trails. This looks really stupid in multiplayer, as there is this weird ghost hopping around on my or my friends truck.
Long story short, if you want to decrease the amount of waiting time.... Tell your buddy to start practicing the works of the crane He'll get used to it.