Dust lanes are gravity's settling test. Gas and dust orbiting in a relaxed galactic potential dissipate energy and settle within a few dynamical times into a flat, symmetric plane aligned with the potential's principal axes; that is what disks are. The prominent dust lanes of lenticular and elliptical galaxies, Centaurus A's spectacular warped band the canonical case, refuse the test: significant asymmetries, warps, and complex morphologies that symmetric settled equilibrium does not allow (Graham 1979).
The standard explanations buy the asymmetry with recency: the dust is merger debris still settling, caught in the transient gigayear between accretion and equilibrium. The purchase strains in two ways. Statistically, asymmetric lanes are common enough that the transient phase must be caught routinely, requiring merger rates at the high end of expectations; dynamically, several well-studied lanes appear long-lived and dynamically ordered while remaining asymmetric, structures that persist rather than settle, which a transient cannot do (van Dokkum et al. 2015 for the structural context). A configuration that is both old and unsettled needs a sustained organizing influence the relaxed-potential picture does not contain.
The standing is a small but stubborn morphology puzzle in the same family as the galactic warps: features that should be transient behaving like permanent residents, in systems whose isolation offers no perturber to blame.