As per the documentation of the BlockDropItemEvent, it looks as if for a multi block break (example provided is a torch on top of a stone block) both blocks should have an event called respectively. However the current behavior is to call one BlockDropItemEvent with the drops for both blocks contained in the list. This is an issue for plugins such as mine where I check for various conditions, save the location of block break event to a set and then on block drop item event check that set and if the locations match, multiply all drops in the list by 2. 

This results in duplicating items that were not actually dropped by the intended block as well as there not being any way to distinguish what block being broken actually dropped what items.