1) the correct use is here:

http://maxb.net/scripts/markerclusterer/fix.html

js: http://maxb.net/scripts/markerclusterer/lib/mappet_fix.js

function : processJson

if (markerCluster && markerCluster.clearMarkers)
    markerCluster.clearMarkers();

map.clearOverlays();

markerCluster = new MarkerClusterer(map, points);//new search

2) demos are here (a) and here (b):

a) http://maxb.net/scripts/markerclusterer/bug.html (i don’t use markerCluster.clearMarkers();)
b) http://maxb.net/scripts/markerclusterer/fix.html

3) time

This post started from a mistake and I’m writing a post to explain it.
Demos are updated with the correct use of clearMarkers (which is bug free).

1. What is the correct use of clearMarkers?
2. What demos are you referring to?
3. When do expect to complete your post?