(This should be a crosspost written with Massimiliano)
It seems that MarkerClusterer has a bug, fixed with this patch (*) written by Massimiliano while we were hunting together for it on this application (now working fine): after the ajax submit and zooming out, the library was still displaying old clusters and markers, because, after destroying MarkerClusterer, the event assigned to GEvent wasn’t correctly removed.
(*) the patch is created against the r1159 version on gmaps-utility-library-dev.
[...] (This should be a crosspost written with Carlo) [...]