Leaflet.markercluster: Duplicate markers

• I’m reporting a bug, not asking for help
• I’m sure this is a Leaflet.MarkerCluster code issue, not an issue with my own code nor with the framework I’m using (Cordova, Ionic, Angular, React…)
• I’ve searched through the issues to make sure it’s not yet reported

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How to reproduce

Not entirely sure, has to do with timing so it’s not straight forward. I think the case that I’m experiencing has the following characteristics: I’m changing the base layer of my map which adds and removes a tile layer. While doing do I change the markers inside the cluster. I have seen a similar stack trace when trying to add a cluster layer when there’s no base layer map so the zoom is not defined or something, but I’m not sure… Image of this issue can be seen here: https://github.com/IsraelHikingMap/Site/issues/582

I do get the following error message.

ERROR Error: Uncaught (in promise): TypeError: Cannot read property '_zoom' of undefined
TypeError: Cannot read property '_zoom' of undefined
    at NewClass._addLayer (leaflet.markercluster.js:6)
    at NewClass.addLayer (leaflet.markercluster.js:6)
    at categories.layer.ts:135
    at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invoke (zone.js:392)
    at Object.onInvoke (core.js:4629)
    at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invoke (zone.js:391)
    at Zone.webpackJsonp.../../../../zone.js/dist/zone.js.Zone.run (zone.js:142)
    at zone.js:873
    at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:425)
    at Object.onInvokeTask (core.js:4620)
    at NewClass._addLayer (leaflet.markercluster.js:6)
    at NewClass.addLayer (leaflet.markercluster.js:6)
    at categories.layer.ts:135
    at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invoke (zone.js:392)
    at Object.onInvoke (core.js:4629)
    at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invoke (zone.js:391)
    at Zone.webpackJsonp.../../../../zone.js/dist/zone.js.Zone.run (zone.js:142)
    at zone.js:873
    at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:425)
    at Object.onInvokeTask (core.js:4620)
    at resolvePromise (zone.js:824)
    at zone.js:876
    at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:425)
    at Object.onInvokeTask (core.js:4620)
    at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invokeTask (zone.js:424)
    at Zone.webpackJsonp.../../../../zone.js/dist/zone.js.Zone.runTask (zone.js:192)
    at drainMicroTaskQueue (zone.js:602)
    at ZoneTask.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneTask.invokeTask [as invoke] (zone.js:503)
    at invokeTask (zone.js:1540)
    at XMLHttpRequest.globalZoneAwareCallback (zone.js:1566)

What behaviour I’m expecting and which behaviour I’m seeing

Number of element in a cluster should no grow when changing zoom level, but every time I change the zoom level more makers are added to the cluster. this only happens once I enter a “corrupted” state - meaning after an error message like the above is generated.

Minimal example reproducing the issue

Couldn’t create on… I’d be happy to help out but I’m not sure how…

Versions:

leaflet 1.2.0 leaflet.markercluster 1.2.0