I have implemented a fix for this. It will be fixed as of the next update (after 1.3.1).
Unfortunately if you teleport the player back into the modshop they re-enter the mod menu, so I've had to make it so they spawn outside the garage. It will only affect those two garages. I made it affect all garages as I don't know if any other vehicles are affected.
I am, at some point, planning to add custom menu for modshops, as at the moment I can't control or even detect the prices etc.