Wrong behaviour media-breakpoint-down() mixin

[4javier]

Arch Linux
Firefox 77.0.1
Bootstrap 4.5.0

I would use this simple class to make an element disappear for viewport's width under 768px.
.my-class { @include media-breakpoint-down(md) { display: none; } }

Instead, to reach my goal I need to pass "sm" to media-breakpoint-down. Considering that I left variables untouched, I thought that media-breakpoint-down(md) should work as expected. Same thing for media-breakpoint-down(lg): it triggers at 1200px and not at 992 as the name would suggest.

I think there's inconsistency with media-breakpoint-up, where i.e. media-breakpoint-up(md) gets triggered when viewport's width reaches 768px.

[ysds]

This addressed in #29148 (v5). But we can't apply this change to v4 for keep compatibility.