Project Cost Allocation don't take the right amount in the source

Summary:

Allocation rule (Incremental method) re-allocates source amounts that already have been allocated (YTD)

Content (required):

1) When I retry generating allocations using the same rule, it takes the source amount already allocated previously and re-allocates it, doubling the expenditure items. From what I read, the Incremental method is tracking what is already allocated and does not reuse the same amounts for future allocations

Can anyone confirm that this is the normal practice and how to prevent this from happening? Thanks!

2) Also, I noticed that whenever I create an expenditure item with a past expenditure date (in previous period), the allocation rule doesn't take it into account as if the transaction never existed.