`mirror: "all"`: spurious ticks

The documentation of mirror states that:

If "all", axis lines are mirrored on all shared-axes subplots. If "allticks", axis lines and ticks are mirrored on all shared-axes subplots.

I.e., from what I gather mirror: "all" should not put any tick marks but merely draw a line. Presently, however, it does put tick marks on the mirrored axis of the first subplot (or even solitary plot).

Previously, a variant of this was noted in #4136 where mirror: "all" would behave like mirror: "allticks". This was addressed in #4140, but the fix seems only to have addressed part of the issue, however. Specifically:

What I thought expected behavior would be is this (i.e. tick on no mirrored axis; only the left-most non-mirrored y-axis of the first subplot):

Reproduziere das Verhalten anhand der verlinkten CodePen-Beispiele und vergleiche mirror: "all" mit mirror: "allticks" bei Subplots mit gemeinsam genutzten Achsen. Verfolge das für das erste Subplot verantwortliche Verhalten der Achsenspiegelung und überprüfe anschließend, dass mirror: "all" gespiegelte Linien ohne Tick-Markierungen zeichnet, während die erwartungsgemäß nicht gespiegelte Achse ihre Ticks beibehält.