I've noticed a small issue with my email client for quite some time now where composing a new email will have several blank lines by default.
It's not too much of an issue to simply delete them but hey, maybe no one had pointed this out before! So I filed a bug report only to get this response... basically it's not a bug, its a feature!
It's not a bug just because the software doesn't conform to your personal preferences. You're asking for what would be considered an enhancement - not a bug fix.
But
why would several blank lines be the default behavior
I don't know the reason. I think not having the extra blank lines would be better, but it works just fine as is - even the post admits this much. That's why it's an enhancement. It's possible for software to be functional and consistent and still have room for improvement - that doesn't mean there is a bug.
It's not about preference. It's about what every single other email client does, including their own on different platforms, and this is even fixed in their upcoming beta of this same app.
My point is that someone made the decision for it to do that and that the software works just fine as is. It's not a bug, it's just a weird quirk. The fact that they made the enhancement you requested doesn't make the old behavior buggy. Your post title said "it's not a bug, it's a feature!", but the behavior you reported is not accurately classified as a bug.