Hi,
if object which will be added to the forest has multisub material assigned ( lets mark it as "multisub A" ), then FP assign its own multisub material ( "multisub B" ) to the forest, and this "multisub B" will have as much materials as is the highest ID number in "multisub A" , so if you have in reality in "multisub A" just 2 materials which one if have id=999 , then "multisub B" will consist of 999 materials. Coudl that be corrected ? This may look as silly request, but in complex scenes with complex multisubs, it`s hard to navigate in multisubs created by FP.