I was using the contextmenu from the sandbox and now I'm using the one from 4.2.0.RC1. With the sandbox contextmenu, when several rows in a table were selected the right-click to open the contextmenu didn't unselect others rows.
The new rich:contextMenu does unselect the other rows. It's quite embarassing because we can't use it to apply a contextmenu for several selected rows...
Thanks in advance,