I have experienced the same...when i moved model , vegetation stayed where it was and erase tool could not do anything cause there was no surface under vegetation.
Dont think there is easy fix to this now. A needed to move my model back, delete vegetation and move it again to new place.
For new verison I hope, there will be possible to control painted vegetation at least like this:
- turn it OFF or ON in scene manager - now when You paint, it have to stay there. Sometimes I would want to make some views without it, then turn it on again for different view
- move painted vegetation with mesh on which it was painted !!! it does not make sense, that vegetation stays somewhere in the space when model is moved - I think nobody expects that
it should not be hard to constraits its position to parent objects, which was painted on