There is some weirds situation when I using simple blast search.
Version of blast is 2.9.0+

When I use the `evalue` parameter of blastp, I think it should be a simple cut off value as the same as others. 
But I found out that, even with the same query and same subject. The evalue could not extract correct sequences at all.

With 1e-38 evalue, I got these sequence without the lower one (1.60e-83)
But if I use 1e-35 evalue, I got this.

This makes me question the cut off/filtration of the blast.

The situation is also described in the following picture.
https://gist.github.com/444thLiao/5d071703f65935c71906a19d39f0187f

If there any need to download the file/db I used. please feel free to download it at [download data](https://drive.google.com/open?id=1PRNs6W2DhbQqKp7jgW7HsI09qvAKzUVn)




OK, this is a tricky issue you mention here, though one that has been extensively discussed on biostars (and other fora / blog posts )

<s>Can't find any links to point to right now, but will look for them.</s>

long story short: the filtering is not done at the end (== reporting stage of blast) as you might intuitively expect but also has it consequences earlier on in the blast process causing differences in output.

EDIT: here is some background info on it :

biostars posts:

 - https://www.biostars.org/p/52787/
 - https://www.biostars.org/p/340129/
 - https://www.biostars.org/p/341227/

a blog post (which kinda started it all):

https://blastedbio.blogspot.com/2015/12/blast-max-target-sequences-bug.html

and a paper on this:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6662297/