The false positive was mainly caused by my initial mistake.

Before explaining the initial mistake that could still be common, and lead others in “error”, I would like to clarify that both rev.1159 and rev.1214 (current) do not contain the bug I thought I had found.

There is no need to patch the library by adding the destroy method.

The library Markerclusterer already exposes a method to correctly destroy the clusters: clearMarkers .

clearMarkers works

The initial mistake I made was to isolate within a function instance

var markerclusterer = new Markerclusterer(map, points);

Having Isolated markercluster in the function called by the form, at each form submit I wouldn’t be able to call clearMarkers methods, not having access to the previously created instances.

map.clearOverlay() is not enough .

You have to remove the clusters explicitly otherwise the first trigger ZoomIn ZoomOut keys of the map would show clusters of the previous search.

To summarize, use the library Markerclusterer

1) before removing the clusters:

markerclusterer.clearMarkers();

2) then wipe the map with

map.clearOverlays();

For those who want to analyze the working code I release two demos that are going to overwrite the previous:

• with a programming mistake not due to the library
• with a proper usage of clearMarkers

Another thing that could lead to errors (more false positives) is that after a zoom in / out clusters might be slightly different.

• many clusters

Searching “Test 2″ you’ll find 3 clusters over the Western Alps

Triggering a ZoomOut and then a ZoomIn, the clusters will be slightly different than before. Increasing the number of clusters it’s clearer something went wrong.

• BUG
• FIX
• PATCH

Carlo and I, working together on this application have met a problem hard to isolate and solve.

Markerclusterer library (of gmaps-utility-library-dev) has a bug.
Let me try to explain the problem.

Each cluster has an event associated with it (in fact, the click event on the cluster triggers the “zoom in” on the map and the cluster splits itself in markers or smaller clusters).
When, from the outside (for example, within a form), I clean the map – map.clearOverlays(); – and then I refill it with a new search, I’m not able anymore to destroy the clusters.
It seems the clusters are disappeared but, in fact, zooming in or out, they come back.
Look at the two following pictures.

STEP 1

STEP 2

ZOOM OUT

The first and second picture shows the clusters correctly.
The third picture instead (demo bug) shows the clusters of the second search AND the ones of the first (after having done “zoom out”).

The whole thing is due to a bug in the JavaScript garbage collection (I suppose…).
The object has been “subscribed” to an event. The object is destroyed but after the first trigger of that event, the object come back.

To fix this strange bug (it’s even hard to reproduce it, without a form!) it’s mandatory to provide to the markerclusterer library a method to correctly destroy the clusters.
The patch (the diff file has been written again the 1159 revision) adds the destroy method.
Before doing a new search, it is required to call

map.clearOverlays();

AND

markerCluster.destroy();

where markerCluster is your instance of MarkerClusterer(map, points);

this.clearMarkers();
GEvent.removeListener(mcfn_);
mcfn_ = null;
me_ = null;

I reported the bug to the developers with a demo of the bug itself (and a second demo with the fix). I hope my patch could help people to not get mad on it.