Bold italic zero not as heavy as other characters

Thanks for your work on this great font, as well as the alt-hack character variants.

While using it, I noticed that the bold italic zero doesn't appear as heavy as the other bold italic characters, or as the bold upright zero. This screenshot shows what I mean:

The first line is DejaVu Sans Mono, for the sake of comparison, and the second line is Hack. Both are in bold. When I toggle from non-italic to italic, it appears that the outline of the zero becomes thinner.

Perhaps this was a design decision, but it stuck out to me, and so I wanted to get your thoughts on it.