See also attached screencast.

To reproduce:

• go to Pulse and select one message
  • UI will correctly display one item selected
• switch to Tasks and back to Messages
  • UI will display no selection but pulse footer states that one item is selected
    Try to select more items and the count will be offset

This can obviously be conducive to confusion and unwanted behaviour, e.g. deleting items you don't actually want to delete.
—
After a quick investigation apchelintcev found out the cause

it happens cause Message class has no equals/hashcode impl
you go back and forth, you reload the Grid, the new beans are queried from the backend => your selection isn't there any longer (why footer isn't updated -> that's the internal logic of the presenter)
just checked the Task class case - same story