This is an old topic, but i have to dig it up again.
I've been trying to clean up my payee list recently.
I found at least one instance where payee names are coming up in Filter that are not coming up in results.
I believe i had asked for the ability to delete payees in the past, and someone said they came from the actual transactions.
That doesn't seem to be the case with the example in the following screenshots:
(1) I filtered all the AARP payees, it says there are three different names:
(2) I was in 'net worth' so this is "all accounts" but only one AARP payee came up in the filter
(3) On new transactions, the same payees the filter function found came up as suggested payee names:
