Thanks for tracking down the chageset that broke everything. looking at what changed I am not 100% sure why but changing:
rcmail.addEventListener('listupdate', function(evt, props) { rcm_contextmenu_load(true); rcm_contextmenu_init('messagelist tbody tr'); } );
rcmail.addEventListener('insertrow', function(evt, props) { rcm_contextmenu_init(props.row.id); } );
to
rcmail.addEventListener('listupdate', function(props) { rcm_contextmenu_load(true); rcm_contextmenu_init('messagelist tbody tr'); } );
rcmail.addEventListener('insertrow', function(props) { rcm_contextmenu_init(props.row.id); } );
in contextmenu.js seems to fix the problem.