It seems there is a bug on the Header Poisoning scan on version 1.4.2. Whatever list I provide I always get the results below.
Seems to be related to this commit bc341a7.
I tried to check the code but didn't get what was the problem.
Doing exactly same command with version 1.4.0 the feature works as expected.

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| Header Poisoning
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Testing 2 headers
Skipping empty header (1/2)
Skipping empty header (2/2)