I am not sure if this is related to a recent upgrade to WP 3.4, as I have only just installed GTM as well, but I am seeing strange things happening on the task list view. When hovering over the name of a task the person responsible disappears and everything else shifts to the left, i.e. Deadline goes to the Project column and Actions to the Deadline column. I have to refresh the page to clear this, i.e. the correct view is not restored when the mouse leaves the DIV.