It' not THAT unusual that you could overdrive a woofer with low bass. 35-70Hz isn't THAT low but they are rather-small woofers.
They might go loud at the mid & high range but you're not going to get "realistic" bass that you can feel in your body.
And typically with active speakers, the bass is EQ'd/boosted to extend-flatten the frequency response downward and that makes it easier to overdrive.
Then, the really-deep and subsonic bass is
probably rolled-off so you don't rattle the woofers with bass that the speaker can't reproduce and/or bass that you can't hear. At very-low frequencies a ported woofer moves freely so it can more-easily move beyond it's physical limits compared to a sealed speaker where it has to compress (and decompress) an "air spring"
You couldn't be any more wrong. Its a defect.
Since it's the same in both speakers,
that would PROBABLY be a design-defect and you probably need different speakers. (But the manufacturer would probably consider it a "characteristic" or "limitation" rather than a defect.)