When using Sakai in multiple tabs, messages can sometimes arrive in the wrong site.

Create two sites, X and Y, and add users A and B to both.
Login as user A and navigate to X
Open another tab and navigate to Y, again as user A
In another browser, login as user B and navigate to site Y.
As user B, send a message to user A. It should arrive in the second tab, in site Y, sometimes it doesn't.