many2one fields in tree-view cause warning message

When entering a many2one field in an editable tree-view, there is a warning message when moving to the next field. The user knows that they haven't entered all the data, but they are prevented from moving to the next field from entering the data by the pop-up warning message:

Warning Message: please enter a value.

This is particularly happening when the user types a couple of characters into the m2o field, and then selects one of the items in the drop-down list. The selection seems to be firing two events:
 * form/on_change: that makes sense
 * list_grid/save: that doesn't make sense (the user isn't done yet, so it shouldn't be trying to save the row).

The two calls messages being sent to the web client by selecting the element in the drop-down list are:

127.0.0.1 - - [21/Jan/2011:15:51:51] "POST /openerp/form/on_change HTTP/1.1" 200 29 "http://localhost:8080/openerp/menu?active=417" "Mozilla/5.0 (X11; U; Linux i686; en-GB; rv:1.9.2.13) Gecko/20101206 Ubuntu/10.10 (maverick) Firefox/3.6.13"
127.0.0.1 - - [21/Jan/2011:15:51:52] "POST /openerp/listgrid/save HTTP/1.1" 200 114 "http://localhost:8080/openerp/menu?active=417" "Mozilla/5.0 (X11; U; Linux i686; en-GB; rv:1.9.2.13) Gecko/20101206 Ubuntu/10.10 (maverick) Firefox/3.6.13"

This example is taken from the hr_timesheet module, where entering a Timesheet in the 'My Timesheet' screen. However, this has been replicated in other editable list views. This problem does not occur in the GTK client.

Trunk Version: 6.0.0
Server revno: 3318
Web revno: 4453