Items are not deleted after filter

[mecoFarid]

The problem stated here #565 still persists in FlexibleAdpater version 5.1.0. Steps to reproduce:

1. Apply filter
2. Delete a single item (FlexibleAdpater.removeItem(position))
3. Reset filter
4. Re-apply the same filter
5. The deleted item will reappear

Note: I have applied both setPermanentDelete(true) and confirmDeletion().