The bug can be reproduced in ZK fiddle
http://zkfiddle.org/sample/oovs9/7-Browser-blocked-on-tree-update

run the example with version 6.5.2 open a treenode, and click a value in column C1 or C2 (in one of the childnodes) -> browser freeze
using version 6.5.1 the browser does not freeze and the value in the cell is updated

http://forum.zkoss.org/question/79555/browser-blocked-conflict-between-threads/